I don't think that is his problem, it shouldn't matter what cable you use unless somehow its changing your in-game aspect ratio. Unless however there is error in the way your gpu is processing in either connection such as a reduction in color processing which would increase performance. After seeing his spec i think we can say his shitty fps is due to his hardware.
Can confirm GTX 760 is a beast. Get on average around 50 (60-80 in campaign and 20-40 in kavala) with a GTX 760 super and i3-4130, which for its price is pretty impressive.
I'm confused man, you cant find a pc yourself that gets 60 fps in arma, so you want someone to comment their specs?
Anyways www.cyberpowerpc.com or www.ibuypower.com are probably your best bet if you don't know how to build your own, but you know somethings about computers. If you don't know what parts your looking for you really need someone to help/talk to you; so you can figure out things like if you want an ssd or if you need more then 8gb of ram exc.