I'm a noob at modelling, so my advice might not be the best. With that said:

It sounds strange that you get lag when working with objects beyond the cube. I've tried Maya 7PLE on an old laptop (1400mhz / radeon mobile 9000 / 256mb (!!!) RAM ) which is far inferior to what you run it on. I had no problems whatsoever creating characters and such. With a bit of hiding inactive objects and such that is. I doubt Maya8 is a lot more resource-hugging in the modelling process than Maya 7. Thats up for the pro's to clarify tho.

My suspicion is that there is something slighty "off" with your computer. Some driver issue or possibly (malware?) processes hugging resources. Paging file on a full/badly fragmented disk?

Maye someone better informed than me can debate this: The 9550 is capable of running games like Unreal Tournament (the original) and thus should have the ability to render an un-textured model unless your polycount is in the 10s of thousands? (Questions, not facts) Modelling 1 character vs rendering 10+ textured/lighted characters in-action. Doesnt make sense to me, but ... I'm the noob

Just doing a little brainstorming so you can really try to narrow down where your $60 should go. If you're lucky, you might even end up spending'em on beers while you model... if it turns out the issue isnt about your GFX card

Nub trying to help nub... pros: have a laugh and give some pointers