Choosing MBP for best performance on fcp

Hi!

I am currently looking to buy a macbook pro, probably 15 inch, for editing video. I have been thinking about buying a second hand non-retina that I can upgrade with SSD and more RAM. However, I have no clue about GPU, and figure that I should be smart about it before I buy as it can´t be changed. Are there any specific recommendations for MBP-models with good GPU well-suited for FCP? Or do they just generally improve as they get newer? I am having some trouble figuring out what would give better value - new computer from apple, or some years old second hand.

I am considering a 2011-model with "HD Graphics 3000 with 384MB of DDR3 SDRAM shared with main memory5", would that be a decent set-up? I don´t have enough to spend on a high-spec new macbook pro 15. I could go for 13-inch, but I understand not having quad-core CPU would be quite the decrease in performance.

Thanks for any advice

For what it's worth...

I have an early 2011 MBP (The first one with Thunderbolt). I use it for pretty intensive work on FCPX, FCP Studio, AE, etc. While it handles everything quite well, the fan is constantly going and I know this thing is working hard to complete the tasks at hand. Just near the end of my warranty, I had a hard drive failure. Then, I had a logic board replaced. Although the specs say different, you can load it with 16Gb of ram.

Not sure how much work you're going to do on it, but it's done the job for me. That being said, I know I don't want this MBP to be my long-term solution. I just don't want it to have to work that hard. As a result, I will probably be upgrading soon. Maybe the next MBP or a Mac Pro...