Black Ops 1 and Modern Warfare 3 both pushed the Wii the hardest. So much that they had to stream the whole map into the disc due to lack of ram. Making the disc spin in override mode.

Many many people had to send their wii to Nintendo to replace their broken disc drive :D

SMG2 does stretch Wii's muscles, but it's not doing quite as many high-end tricks as something like Conduit 1  & 2 or Jett Rocket.

Same for TP and WW compared to RE4 or the Rogue Squadron games.

SS I found pretty unremarkable technically.

SMG running at 60fps? Skyward Sword? Mario Sunshine with its water simulation? Pikmin with it's huge number of friends and enemies on screen? Twilight Princess just being gorgeous? Metroid Prime? Ocarina of Time? Kid Icarus: Uprising?

I think they push their systems harder, and more consistently, than any third party. That's why this gen has been such a big disappointment. Third and second parties are pulling a lot more out of the Wii U than Nintendo is.

So far, I'd say so, yes.

To date, it's one of only 3 games on the system that's even confirmed to be running above PS3/360 spec.

I sort of agree / disagree with that statement... Nintendo is the best when it comes to maximizing the performance of average hardware or somewhat limited hardware, but that's mainly because they tend to withhold alot of details about the inner-workings of their consoles from other developers, as well as developing their own hardware workarounds / solutions like the Super FX chip and N64 RAM Expansion Pak, putting third parties at a big disadvantage compared to Nintendo and their 1st/2nd party studios. Take each console for example:

NES was based on technology from the early 80s (it was originally released in summer of '83 in Japan), yet Nintendo and a handful of other developers managed to design colorful, artistic games for it well into the 90s like Mario 3 and Kirby's Adventure just to name a couple. Some developers like Rare (aka Tradewest at the time) actually reverse-engineered the NES in order to design games for it, which is why there games are of a notable quality above your typical 3rd party NES games

The SNES had a notoriously slow CPU... Nintendo remedied this by designing the Super FX chip, which only a couple of 3rd party titles (most notably Doom and Mega Man X2/3) were able to utilize during the SNES's life. And then of course Rare had access to ACM workstations that allowed them to develop DKC and KI for the SNES which were leaps and bounds above any other SNES games in terms of visuals at the time.

The N64 was of course the last cart-based console, and was known for its bottlenecks in hardware design. Most early 3rd party titles frankly looked like ass compared to Nintendo and Rare's stuff with a few exceptions. The Expansion Pak was later introduced which was required for certain Nintendo / Rare games, and some 3rd party devs were also able to take advantage of it with noticeable bumps in resolution but not quite to the effect that Ninty / Rare and Factor 5 with Rogue Squadron and Battle For Naboo were able to achieve.

GameCube... aside from Nintendo and Rare, Factor 5 also had access to early prototypes of the GC when they were designing Rogue Squadron II and they even helped develop their own sound and graphics tools for their GC games. Again, this put them at a distinct advantage over the competition, with Capcom's REmake and RE4 being some of only a handful of 3rd party games to push the system.

Wii / Wii U... lets be honest, at this point most 3rd parties stopped caring about pushing the consoles and just cared about making a quick buck off of stuff that would sell like minigame fests or dance / music games. Other than Conduit 1 & 2, and maybe Xenoblade, nobody other than Nintendo really pushed the Wii's hardware.

The jury is still out on the Wii U, but unless someone like Retro develops a realistic-looking title that requires the hardware to be pushed to its limits instead of the typical colorful Mario / DK stuff that they and Nintendo have been putting out on Wii U, it's still going to be treated like a "last-gen" console in the hardware department.

It's not just the RAM they push; the elaborate setpieces and huge numbers of AI characters they run at once, each with squad AI, ragdoll physics, and tons of different animations, push the hell out of Wii's CPU.

If we seem to be counting Retro Studios for stuff like DKCR, why not Rare for things like DKC?

Anyways...

NES: Kirby's Adventure
SNES: Mega Man X 3, Yoshi's Island, DKC2, Street Fighter Alpha 2
N64: Banjo Tooie
Gamecube: Super Mario Sunshine. Crazy how overlooked this game gets. The water effects and draw distance are absolutely insane. Resident Evil 4, Wind Waker.
Wii: Donkey Kong Country Returns, Xenoblade, Monster Hunter Tri
Wii U: Super Mario 3D World
Game Boy Advance: Golden Sun, Street Fighter Alpha 3
Nintendo DS: Kingdom Hearts 358/2, Phantom Hourglass, Ninja Gaiden, Wizard of Oz Beyond The Yellow Brick Road (seriously)
3DS: Kid Icarus Uprising, Kingdom Hearts Dream Drop Distance, Mario Kart 7

With the excepton of Skyward Sword, which I see nothing impressive about, those games did indeed make good use of the hardware, I'd simply contend that the games I listed use more processor-intensive tricks.

I'm not saying Nintendo never pushes their hardware at all, many of their games do, just that I don't think they've taken the absolute top spot for any of their consoles.

Rare were second party, Retro are first party.

Well, aside from the wii and u, nintendo always launched with the technically most impressive games for a while. Especially mario 64, it took years for that game to be matched/ surpassed. It seems lately that nintendo has gotten a bit lazy though. Their 3ds games are pretty nice, and mario 3d world, but other than that, they really havent done much lately. Id love to see them put the time and effort that they used to do for games like mario 64 and ocarina of time. If they did that, I belive they would make an amazing game, both technically and aesthetically.