y-koron said the 250K was their week 1 not lifetime prediction.  Since he's the one who speaks Japanese and we got it off of a badly translated article I'm inclined to believe him. 

Read the notes from above concerning attach rates... Yeah, GT series sold millions but was between 7-12% attach rate for the install base at the time. The Various MK series were between 18 and 30%, again, based on the numbers posted above. On just attach ratio alone, MK will win in a big way. I would compare the Wii to a Gamecube in terms of purchases of the game so I'd look for Mario Kart DD (cube) at 30% attach as the minimum on a global basis. (assuming the game is very, very good)

Assuming the install base remains the same percentage difference as it is now, on a global basis until both games launch, MK will sell 2.3X more copies of the game assuming an identical attach rate. If the historical attach rates hold, then that number will be even higher... 4-5x more copies...

Again, I'm not knocking GT5. From all accounts it looks like it is going to be a stellar game but I just don't see the numbers justifying a snowball's chance in hell of GT5 outselling MK by any stretch of the imagination.

Mario Kart. Not only will it sell more, but it will be ridiculously fun.

 [realistic racers SUCK]

From what I can tell, a significant portion of GT's fanbase is fairly casual. This component of the fanbase is much more likely to be turned off by the PS3's price and much less likely to buy a driving game if they already have another one they're happy with.

While the various Xbox 360 driving games haven't done nearly as well as the Gran Turismo series, I think it's possible that they may have drawn away some of Gran Turismo's fanbase.

GT5 will have much higher initial sales and possibly initial attach rate, but there's little doubt Mario Kart will crush it lifetime.

GT4 only outsold MK:DD by about 2m dispite having a userbase 10x the size. How could GT5 compete when the Wii will have a much larger user base?

Also a lot more racers compete directly against GT (especially on PS3) than there are that compete with MK. MK also appeals to a larger user base, something Wii specializes in.

I doubt MK will have the 30% attach rate MK:DD did on GC, but even with a 10% attach rate it'll still beat GT5 handily because of respective installed bases.

I believe M$ put Forza in the 360 bundle just so that lots of people would already have a HD racing game before GT was released...... anyone think that could be right?

At first I would say close call, but considering PS3 's userbase and software sales I expect Mario Kart to win by a large margin. However I expect a GT6 to outperform GT5. I believe Mario Kart Wii will be the best selling Mario Kart yet due to a bigger userbase and online play.

Mario Kart Wii: 12 million
GT5: 7 million
GT6: 9 million

I would say Mario Kart, since that game targets on everyone, women, men, children, adults, casual, hardcore gamers. Gran Turismo kind of targets on one part of the audience only, mostly male hardcore race fans.

Why did GT4 sell so much less than GT3? Been wondering that I have them both and liked GT4 3x better... Is it possible that the popularity for GT is not what it used to be(8 million is still hecka popular)

The problem with GT5 is that it is launching so late in comparison to where the previous best selling titles landed with their respective consoles' debuts, so it will have a lot of competition. For example, one of the reasons GT3 A-Spec did so well was that it was available within 6 months to 1 year after the launch of the PS2 in virtually every territory, and there were few (arguably even any) other racers on the platform of comparable quality during that window. Heck, there wasn't a comparable racing experience on any other platform either. Simply, if you wanted a great racing sim, you bought the PS2 and you bought GT3. Look at GT4 in comparison, which didn't even do 60% of GT3's numbers once the PS2 market was saturated. I mean, GT3 launched to an install base of 7-8M, GT4 launched to 10x that number, between 70-80M, with the console at half its original price, too, and barely made it past 58% of its predecessors sales total.

This time around, if there is one genre that is well represented on the PS3, its the driving games. There must be 6 or 8 downloadable demos in the store now (Motorstorm, DiRT, MX vs ATV, NASCAR 08, Carbon, Pro Street, Burnout Paradise, etc ... etc ...). I'm not saying any of these title are a true substitute for what GT5 will deliver, but I think the glut of driving games, and the defection of former PS and PS2 owners to the XBox 360, will ultimately cannibalize GT5's sales -- costing GT5 millions of units over its life.

Mario Kart Wii, on the other hand, is in the opposite position in that (while there is no shortage of racers on the Wii, either) it will enjoy having the market virtually to itself in the category of Nintendo Wi-Fi enabled racers.

With online, Kart will be a monster.