bottlenecking might not be the appropriate term, but if your friends GPU is actually slower than yours(often times a matter of opinion, compare actual specs and amount of ram), next thing to compare is mobo hardware. compare CPUS, he could just have a faster CPU than you, maybe he's got a quad core AMD, AMD's kill it on the floating point math. it's true. ;)
Does he have more ram than you??
Are his harddrives faster than yours??
Is virtual ram a factor?? that **** slows everybody down, i turn it off on any computer with 4GB RAM or more.
is his OS better tweaked out than yours. maybe he's got a lot less garbage running in the background like turned off services, and a bunch of features and applications running in the systray.
and last but not least that slow *** PCI-e slot of yours. that's gonna hurt your graphics performance a lot. if he's got pci-e 2.0 and you only got 1, and his actually being used to it's full specifications, then yes he's gonna have an advantage over you.
however you have good hardware i see there, and if your operating system was cleaned up, you shouldn't have problems running those games.
I've always been that guy that ran high end games on slower machines, cuz i always knew what i was doing. tweaking out my OS and my hardware to the max, and squeezing every little bit of speed out of the OS before launching the game. other people with much new PC's always lagged behind, cuz they leave so much garbage running in the background that they're not aware about. try finding some tweak guides online for gaming. turn off all your windows services you don't use, or don't need(research them), if your PC and not a laptop you can always move the games to a different harddrive, if you have to have your virtual ram on move that to a different drive too, if youre on a laptop, strip that OS down, and squeeze out everybit of speed you can from it, so the game has more resources to run. you can also turn up the games priority through the task manager(becareful about going real time, you could lose control of your computer). but again, if your card is pci-e 2.0 and your slot is not, don't expect to get the maximum performance out of your graphics card until you upgrade that slot.
if you're gonna game, always tweak out your operating system, unfortunately windows 8 is one bloated piece of !@#$. downgrade to windows 7. if it were up to me I'd still be running XP, but software demands force the windows 7 upgrade. no DX10 and DX11 for windows XP. 8(