I'm looking to build my first PC, a HTPC actually. I was considering building it to be future proofed for 6-7yrs with an I7 3770 and a GTX 670 for gaming and multitasking until I realised TV's only input 60hz (60fps). That said, it would probably future proofed for 9-10yrs with a max of 60 FPS. So would it be cheaper/wiser to go cheaper I5 3570 GTX 570, then upgrade in 3-4 yrs or is the 3770/670 the better choice in the long run? I realise its hard to know what the future holds. In a couple years TV's might accept a true 120hz, or monitors might come in 37"- 42". I need your guy's opinions.
That's wrong. Hz and fps is not the same. Most LCD monitors has only 60 hz refresh rate (except for the rare and new 120 Hz LCD out there), and the fps is certainly not limited to 60 fps. Might wanna check your source.
and the latter with changing your tv mode to "game" or "PC", or simply disable every post processing features on your TV i.e; auto contrast, de-juddering, etc.
note both are not 100% guaranteed.
as for future proofing; keep your expectations low. 9-10 years is impossible unless the next gen of gaming consoles REALLY drags us back. 5-6 would require you to OC your components, and even then, don't expect it to perform as the best CPU/GPU available in the market then. 3-5 years is as good as it's gonna get with a non overclockable CPU.
as for your case, i really suggest you reconsider to either get a case that can fit in a GPU longer than 270mm or a GPU shorter than that. most of the 670 i see are more or less within that length and it may very well be a tight fit at best.
In one way of looking at it, it's true that a 60hz monitor can't process more than 60fps. The frames get generated into the card's frame buffers, but the monitor is limited to only being able to read the buffer at it's refresh rate.
In that sense, having the capability to do more than 60fps is not helpful. You ideally want a card which will play at your expected resolution, with very high quality settings where the minimum frame rate never drops below the expected refresh rate ( perhaps tough to do at 120hz, but perhaps achievable at 60 hz.) And you would like that to be true for a few years of games ideally.
Admittedly, at some point attempting to future proof is pricey and maybe pointless. For example, it might be cheaper to buy a well performing card from last years model line at a good price. With the money saved, you can get another video card every 2 years or so as needed that once again, gives you reasonable performance for the games being played.
If you are only using the HTPC for content, and not for games, I don't see where a higher end video card is needed, but I am not an HTPC expert.