Upgrade from HD6770

Hey guys, would like to hear some opinions about this.

Current setup:

i5 2500k OC'd to just a modest 4.2Ghz

Radeon HD6770

8gb 1600 RAM

I got a deal on a Corsair TX550M PSU that is coming soon, my current one is aging and I found out wasn't amazing in the first place. After that, I was considering upgrading my GPU to an R9 270X, mainly because the price range for dropped recently to ~$100-125 (on ebay and amazon).

I am aware that FSX sees more stability with Nvidia cards, but I also want to play other games such as Battlefield 3 and 4. I don't have much of a reference point other than statistics right now, but the 270X beats out my 6770 by roughly 130% in benchmarks.

Would the 270X be a good improvement on the 6770 or is there something else worth looking into?

I was also hoping someone could shed some light on the Nvidia point of view. Are the benchmarks irrelevant to actual performance? Are those Nvidia cards much smoother in gameplay in FSX (over a 270X)? Is there an even better card in the $100-125 range (maybe a 660ti)?

Thanks in advance.