I do most of my work on a CyberPowerPC gaming desktop powered by AMD's 4300 Quad-Core processor (3.80ghz)...and I use it for pretty much everything; music, design, videos, occasional gaming). Got it for around $800 on walmart's website about 2 years ago...not bad for the price. I think it had 8gb of standard RAM installed originally, but I upgraded it to 16gb of Crucial Ballistix Sports and noticed a significant difference in performance (if you haven't upgraded your RAM and have the ability to, I recommend it).
This thing handles most tasks pretty well. It definitely handles Ableton better than any other computer i've owned (but i've owned some pretty shitty computers in the past haha). I'm working on a project right now that has about 26 tracks - a few drum racks, several instances of massive, instrument racks, and one or two more VSTs. Very little mixing, effects/processing plugins in use right now and it's running smoothly. ...When I get to the point where i've nearly doubled my tracks and I start slapping more effects and plugins around that's a different story haha. That's when things start to get pretty choppy for me.
Kind of surprised to see you say it starts to get choppy on you with even smaller projects, since you're on AMD processor that's more powerful than mine. Do you do anything to maximize your processing power during a session? Sometimes when my projects start to get beefy I pop open my dock and task manager and make sure there aren't any unnecessary programs running in the background. ...Can't quite say that makes a worlddd of a difference, but it seems to help at least a little bit haha.