In an interview Taya said that he designed the Raptor with enough strength to handle a 50, and the head is designed to be run up to 2500 rpm's(Don't know how long though).
Every heli has issues, that's one of the reasons to find someone in your area to help you or to see the heli fly for yourself and of course check here for information as you are doing.
A 50 size is a good comprimise between a 30 &60, but I personally stay away from hirobo products because of the shuttle parts pricing debacle. They were charging more for shuttle replacement parts than for bigger heli's like the GPH.Burn me once and chalk it up to experience, burn me twice and then it's my fault.
If you go for a 50 size, only get the OS as it doesn't have the carb issues that others have and doesn't require the break in time that an ABC engine does.
Whatever you get, the most important thing to do will be burn fuel. Once it is setup correctly fly it that way until you have the basics down.
A fury 50 basic is what I would recommend if you are serious about this heli stuff.
A Raptor 50 would be my second choice.
A Sceadu 50 would be my third choice.
A Century hawk 4 or Raven 50 would be my fourth choice.
YMMV
VD