That would be why I guess, my CPU is slightly faster but not by much at all, but my gpu is HD 7750 which is very much slower than your amd gpu clearly, but you say you separate your mesh, how is that possible ?
NOt sure I should be asking about this given this thread wasn’t about blender as such, but if nothing else maybe you could steer me to a video or wiki page showing how to separate a object, though mine is very complex so I’m not at all sure I could do that.
Cheers
nl
I have no idea why it works 
It is very easy to separate your object/mesh,just go in edit mode,select the parts of your model that you want to separate,press P on your keyboard and select “selection”.
And if you want to join them again go in object mode,select the objects that you want join and hold CTRL and press J .
It would help in a pinch but its a nuisance 
If I do that though, when I join them, the irregular area I select, and the rejoin, shows up in the conbined mesh, does that make sense
Anyway this should prob. go in modeling , if there even is a topic for that, but anyway ya it works, with the caveat as I just mentioned, which is just isn’t workable. I can show a image if you need it.
TY
nl
I’m not sure if I understand you correctly (I don’t speak English very good 
)
If you join 2 object they will combine together.
While I am modeling I keep my object separated and when I need to export it I just join them.
Its a tad hard to explain: I chose with lasso, a irregularly shaped area, in which I was doing some testing to see how it goes, and when I tried to c tl J them back, it joined them, but I could see the area I lasso’d clearly which wouldn’t work very well as you can imagine, I hope that makes more sense.
Interestingly enough, and I wish I had it here on my desktop, my intel i5 based thinkpad, does have less lag enough to prob. make this much more doable , sadly its a 14" thinkpad, vs my 24" desktop monitor, so it won’t work except for smaller meshes 
I guess I need to upgrade to at least an i5 to make working with such things easier, but alas as expesnive as C4d or maya are, they don’t cause the slowdown blender does at all, too bad they are prohibitively expensive for us average poor devs ;)heh
Kinda sad really, maya which is my fav. rotates great, very fluidly , but then as noted it slows way down when I try to select verts or faces or edges in the pie mode, just stunning for a app like that and asking on their forums, yielded zero answers, also stunning.
Also, the trouble with separating, is that it would be a hastle given I’m always working on different areas of mesh,but in a pinch it would be better than nothing until blender fixs its viewport lag.
Take care and ty
nl
I understand now 
One more useful shortcut is F.
Select two edges that are not connected,press F and that will fill the gap between two edges.
Yes, I’ve used F and tons of other handy things which work great in blender, at least that much I’ve enjoyed, I just need a faster viewport until I can upgrade at least and they are working on it, but it wont’ be ready ( editing and vertex painting according to BA forum, aren’t ready) for 2.76.
Cheers
nl