I currently have a laptop that is running Intel Core i7-3537U @ 2.00GHz with a 500GB hard drive and 8GB of RAM. I'm a moderate gamer, so I don't game a lot in comparison to the many other gamers out there that dedicate hours to gaming. My computer lags a bit when running source games such as Team Fortress 2, Left 4 Dead 2, Counter Strike: Source, and Garry's Mod. I also like to donate computer resources to Folding@home, so ever since I started folding, it lags more. I like to chat with friends on Skype while running Steam games, so I don't want voice quality to be impacted. I also occasionally slice 3D prints, so I need to have a computer capable of doing that quickly.
Performance quality is my priority, so if a build under $800 is unreasonably, I can wait until I can increase that budget.
My question is, what can I get for $800 or less that will support all my needs as stated previously? Again, performance is my priority, so in terms of cases, lighting, etc. Yes, I would like to make room in my budget for a fancy, lit-up case, but it's not needed.