If I buy this Corsair 750W Modular PSU, will it be powerful enough to last for the next few years? For example... if I decided to build a new PC in a few years, would it power something like two DX11 cards and everything else in a system?


600W would be more than enough...
It would power something similar (or the DX11 version) to the GTX 285, but it may not power 2 Dual GPU cards. It is otherwise a good PSU.

I never know what psu to go for myself as it seems everyone has a different opinion, above superewza stated that 600w would be enough to run what the op stated as two dx11 cards, so crossfire/sli, whereas ripped stated that the 750w the op is intending to buy might not even be powerfull enough for crossfire/sli![]()
I think it's just mixing up maximum/recommended/used.
I'd recommend 750W, but the system would probably only draw 600W at load. I wouldn't risk using a 600W PSU in case of a spike. Besides, the lower the power draw compared to the maximum capacity, the more efficient the PSU becomes (to a certain point anyway).