I found PFPX pretty good, over 3 flights where within 500lbs of fuel diffrence at the end of the flight compared to the calculated estimate.  so long as you put in the wind data (can be copy/pasted if you have activesky which is a blessing!)

 

Again if you give the FMC all the data you have its pretty accurate also.

Topcat performs fuel calculations for your route. PFPX was never meant to take the place of Topcat. It works in conjunction with it.  But right now Topcat has not been updated to do the calculations for the 777.  Have you never calculated fuel with Topcat? It's one of the software's primary functions.

I just use www.fuelplanner.com and round up to the next 5000 pounds of fuel just to be safe and I always end up with about 10% in the tanks

Woc, as mentioned, here's the ETOPS related tutorial you might find useful:

 

http://forum.aerosoft.com/index.php?/topic/73453-pfpx-etops-pmdg777-a-short-guide-p1/

http://forum.aerosoft.com/index.php?/topic/73486-pfpx-etops-pmdg777-part-2-flightdeck/