Need help upgrading MBP

Hi,
I've decided to upgrade my MBP. I currently have a late 2011 MBP 15", 2.2GHz intel core i7, 4GB, 500GB. I major in graphic design at university, and my current laptop is fine, but in the last few months, I've noticed it starting to lag and have a hard time keeping up with tasks in programs, such as Illustrator. I'm deciding between the new 2013 MBPs, but am unsure which one to buy. Is there much difference between the 2.0 and 2.3 GHz? Do I need a lot of RAM? There's a bit of a price gap between the two models, but I am mostly concerned about what will make the computer faster and if there is much difference between them at all.
Thanks.

Your current machine is more than capable for the tasks. I would up the ram and posibably install a SSD. (about $500 for a 240 GB SSD and 16 GB ram) I have the 2.5 Ghz 17" (late 2011) with 16GB ram and a SSD and it can handle all the Photoshop and large files I throw at it. I also took out the optical drive and installed the spinning drive in the optical bay for additional storage or backup. Check out OWC for more info on this. I used their data doubler to put the spinner in the optical bay but opted for an Intel 6G SSD. There were some problems with their SSDs in that model but the Intel has be perfect. The ram is a no brainer and easy to install and if you want to keep the optical drive, switching out the spinner for a SSD is easy as well. You can get an enclosure for the spinnning drive you take out and have an external to boot. OWC has videos on how to do all of this, Including installing the Data Doubler. Oh... I don't work for and not associated with OWC but I have found them to be a great resource for all things Mac. They know their stuff!

One more thing... Try running Onyx (free download) It can help speed things up sometimes.