I thought I would share my findings. I recently bought a late 2014 iMac with 500GB SSD drive, 16GB Ram, and the i7 4 Ghz processor. I couldn't find much in the way of filevault performance on this specific machine, so I thought I would post my screenshots to share. All in all, I'm very impressed. Filevault 2 hinders the performance very little in return for full disk encryption. The screenshots are below. Quite impressive imo 
Brand new computer with nothing installed:
Post encryption:
Brand new computer with nothing installed:

Post encryption:
