GTX 670 is faster than 7850, the only radeon card that can top it up is 7970 or the GHz Edition. The one that is none-reference. If your on gaming, the i5 3550 is enough because of the quad core, if your an overclocker and you want better performance in rendering or editing, then an overclocked cpu is for you. I saw alot of review that compares GTX 680 with GTX 670 for a $100 less with 5% comparison, if you overclocked the 670, it will outperform the 680. So your best bet is Nvidia.
i5 3550 won't be easily obsoleted, because the games are just needing a maximum of 4 cores which is quad core. The one that becomes obsolete is the dual core. That be perfect, besides that 3550 is an Ivy Bridge and it's the newest chipset of Intel. So there won't be a problem.