I also practiced with Barron's and the Powerprep software. The scores I got from both softwares seemed jumped around a TON. I think my practice scores ranged from 1100 to 1300. I got lucky in that my actual score exceeded even my best practice score (1400). Still not sure how that happened, but I think it was a good mix of luck and practice.
You are at a HUGE advantage having taken the test before. Hopefully your nerves will be a bit calmer as a result. My tips for relaxing on test day:
1. Allow plenty of time to get to the test site. Account for uncontrollable elements, like traffic and weather.
2. Eat something! Especially if it's a morning test. You don't want your stomach growling in the middle of the test.
3. Do some practice problems in the morning, just a handful. I forget where I read this, but someone made the point that you don't want the first GRE problems you do that day to be for real.
4. Probably the biggest thing- RELAX the day before. Hang out with friends, go for a walk, watch a movie. Do ANYTHING but study.
Hope that helps, and good luck