well if you won't consider Intel, the FX 8320 is likely one of the ONLY choices you have, since AMD's new line up for 2014 consists solely of APUs and lower power tablet/mobile processors. however, an FX 8320 is fine and can stay competitive for quite a while if you give it a nice overclock with a compatible motherboard and a decent air cooler.
and a R9 270x crossfire is enough, in the future crossfire can only get more stable, and a R9 270x crossfire has shown the potential to match the R9 290x, so that's very good and will likely be enough raw performance for a long while imo
but like other people have said, there's no way to predict beyond even 2 years, as technology moves fast, I'd say that you'll be fine though, maybe not for 5 years but for 3 or 4 no problem, there are still 3/4 year old Phenom computers out there still kicking and scratching