No actually the FPV Community on RCG had a debate and voted on a couple numbers. If you'd like to muddle through the thread I'm sure I can dig it up. Trust me it was a messy debate. Many argued that a Easy Star can fly 80mph down wind in a dive... The 60x10 numbers was the middle ground we came up with and submitted to the AMA. Granted most people that fly FPV are using foam models. The idea was to allow some room for growth. The 60x10 number will allow a very well equipped '60' sized trainer with FPV gear. We didn't want someone taking a 15lb jet and flying it via FPV at 120mph. There really is no way of knowing how fast the plane is going unless you have a OSD displaying ground speed from a GPS. So with that in mind there will be some self regulation on the FPV'ers end.

Keep in mind the "Suggested AMA Field" is roughly 23 acres. Do a bit of math and tell me how fast and how big of an object you want maneuver in that limited amount of space. Plus these are numbers to start out with. Once FPV is out in the field for a bit, the numbers can be looked at again.

Threads where numbers came from..

Max Speed:
http://www.rcgroups.com/forums/showthread.php?t=892878

Max Weight:
http://www.rcgroups.com/forums/showthread.php?t=892862