Borderlands 2 not as optimized for AMD...?

That's quite possible Shim. It might help if you play around with the config tweaks though...

https://koitsu.wordpress.com/2012/09/29/borderlands-2-performance-tweaking/

Sometimes just changing the right one can have a very dramatic effect in the positive direction for certain cards.

former Radeon since a while AMD HD 7800 Series isn't an exact type of GPU ...
judging the config i doubt the CPU slows your game down at any point

I don't think you should expect more FPS with Radeon HD 7800 Series graphics card.

You didn't specify the precise GPU. Why's that?

Whenever you hear the nVidia tune at the start of a game, you can be sure that it is indeed gimped for AMD cards.
And since Borderlands uses Unreal Engine, which is so made for nVidia they should rename Epic to Team nVidia, it'll run terrible on AMD cards, yes.
If it is a consolation, since nVidia forced PhysX into the game, it runs terrible for nVidia users too when that is turned on. (Plus results in hilariously frustrating clipping glitches.)

Specs:
OS: Windows 10 64 Bit
CPU: AMD Phenom X6-1090t
RAM: 8 gigs.
GPU: R9 270x

60 +/- FPS

To be honest, there is no game optimized for AMD. At best you can get comparable experience.

Nvidia always owned GPU world, and will still be doing this.

AMD is not really optimized for games. It is price/performance.

You didn't specify resolution and settings, and AMD is fine, performance varies with setup, model, drivers, and game, just like every other component and brand.

That performance sounds pretty good actually.

The 7850 is an older mid-range GPU... it has the same performance as a five year old GTX 480.

I can play it very good without PhysX, and even with PhysX if playing alone on Tiny Tina DLC, Bordelrands 2 is a good optimized game, and I have Fx 8350 and Radeon 7950, no problems. Playing with PhysX in multiplayer is impossible.

Lower your resolution. I have a Radeon HD 7750 (with 1 GB RAM DDR5) and it has solid/constant 60 FPS with VSync at 1366x768, and even in higher resolutions up to 1600x900 with everything maxed (with AA at 4X and AF at 8X).

(My system: Win 7 64-bit Home Premium / Intel Core i5-2500K 3.3 GHz / 8 GB RAM).