I'm gonna say no. Wait till 4K becomes cheaper/norm. Because the eariler models of this stuff ends up having missing features/functions. Everything's updated all the time. And it's not worth it. I'm personally done caring about resolutions. And rebuying stuff.

Sony XBR55X810C has a low input lag and response time, as well as having some of the best upscaling in the industry. They're listed at $998, and if you're in the US near a Fry's Electronics, they will pay the sales tax (ignore their protection plan pitch, Sony's is cheaper and covers more in addition to having a higher end that converts accidental).

Device best suited for its situation 

I'll be exploring the wonders of projection sometime during this year, with a cheapo hobby home theater room in the basement.
Not really possible to empty the wall, so I have to invest in a projection screen... any advice there?

If I had enough money I would buy the 4K TV.

4k starts at 40 inch, but I would recommend above 47 inch for 4K. But hey I think your image of a big tv is different from me. I think 40 inch is normal, 50 perfect,  60 too much, 65 way too much.

It depends what you want to spend on it.

For my first projector I simply white washed a wall, currently I have a fixed Clarion screen.
Since you're in the basement you should not have any problem with amient light, which means you can ignore all the fancy silver or high gain screens, anything white will work. Even spanning a white sheet between two long slats will work. Couple pieces of lathe wood, blackout cloth and staples are sufficient. There are plenty guides and tips online, simply search for do it yourself projector screen.

Here's a comparison between DIY and an expensive professional screen, as long as you keep the lights off there is hardly any difference. http://www.projectorcentral.com/diy_screen.htm

Anyway if you don't want to bother and still end up with a non collapsable screen, something like this will do the trick too
http://www.bestbuy.com/site/elite-screens-tripod-series-100-tripod-projector-screen-black/9633731.p?id=1218134579595
Or this if you can hang it from the ceiling
http://www.bestbuy.com/site/elite-screens-manual-series-100-pull-down-projector-screen-black/9622592.p?id=1218132469398&skuId=9622592

I'd say if you have the money, get 4k. Just make sure it's a good TV. I saw a suggested $600 4k TV. Surely that's rubbish. You don't want to be regretting the purchase for years.

4k tvs have a bigger input lag, if the main purpose is console gaming, i would go for the 1080p, if a all around media, get the 4k. 4k gaming with that true resolution is still far from us and don't believe all these ps4.5 rumors, grain of salt? More like a full truck of salt...

If you're going for 4k, don't go budget. Get a good, slightly expensive model. You're better off getting a really nice 1080p tv rather than going for a budget 4k model.

http://www.bestbuy.com/site/samsung-55-class-54-6-diag--led-2160p-smart-4k-ultra-hd-tv-black/4213306.p?id=1219707301732&skuId=4213306

This is the set I have my eye on currently. HDR isn't supported on the older models but Samsung has a firmware patch coming soon or already for the older ones to download and support it. HDR is needed for 4K blu Rays.