PS4 Pro...

I was under the impression that 46" to 70" TV's were actually 1080P when advertised as 1080P, and that anything smaller was actually 720P regardless, even though they called them 1080P, since a smaller screen doesn't need the higher res a bigger TV requires to look as crisp and clear.

For a 26" TV, at best it scales 1080P down to 720P, but maybe even 540P?

I'm with LivingMetal on this one. There will be a very slight upgrade with Pro in terms of eye candy on that TV, but mostly your only going to notice the smoother FPS and potentially faster load times. Pro will be future proof as well, if and when you want to upgrade your TV though. There is also the optical audio out to take into account. Whether that's worth a hundred extra to you now at the store, and double or more, the power usage cost each year, is your decision.

With your 1080P TV, the Pro shouldn't have to push that much harder to show steady 60FPS and full HD, but for 4k, it will probably use considerably more power. I wouldn't be surprised if Pro uses more than double the power of Slim with early 4k games because like a PC, the dev's should simply be able to use the extra horsepower right now to push out the extra FPS and eye candy without having to optimize all that much. It depends on how long they have had to play with the new tools and how familiar they have become with them. Regardless, the games should eventually get better optimized going forward for Pro, and use much less power, but I would suspect that not to be the case early on. 

I have a 50" plasma and I won't be upgrading to Pro unless PS5 is much further out than I expect. I wouldn't be surprised to see it fall 2018, fall 2019 at the latest. I'm a semi-hardcore gamer I guess you could say. Not quite casual, not hardcore though. PS4 is enough for me.

They called them HDTVs, all 720p, 768p and 1080p tvs are all HDTVs, although they used full HD for 1080p. Of course you also had misleading adverts that it would accept 1080p input, especially with projectors. And now again with 4K. Many of the so called 4K projectors actually have 1080p 3lcd with pixel shift technology. With 4K tvs you also have to look out for accepting HDR and 10 bit input vs actually having a 10 bit panel and the brightness to render the full range of HDR. Anyway that's what the internet is for, stores are useless.

Few simple questions to ask yourself if you'll benefit from the pro: Are you annoyed by frame rate drops and or aliasing issues. Pro should run at a more stable frame rate and provide a cleaner image with supersampling. It doesn't matter how big or small the tv is, jaggies, pixel crawl, moire patterns and flickering lines can still be seen. I assume you're still close enough to be able to play the game :)

Jaggies and some frame drops don't bother me on my 1080p projector, I'm buying it to get the best out of psvr. Yet I'll admit that getting a pro version of TLG is a very nice addition.