Hey Budgiesmate,
My apologies if I'm wrong but in reading between the lines, I've assumed that this is your first heli(?), and made my comments with this viewpoint.
First, I'm wondering what exactly you meant by "...when it repeatedly went off and did its own thing despite my attempts to tame it". Flying a heli requires constant input, so much so that I personally don't feel comfortable taking my fingers off the sticks to even scratch my nose. A micro heli will generally speaking be even less stable. I'm always surprized when I do switchover between the two, the gasser(ie nitro bird) is so much more "relaxing" after a session with my micro.
I'm not sure why you are not getting full revs, perhaps a radio setting problem, or could be a battery that is not fully charged. Also not having the rotor spool down immediately is normal, which can take several minutes on my gasser if left alone, and won't be fixed by going to a Futaba radio.
So, personally, if I've read things right (again, my apologies if I haven't), I feel going with a new radio will not solve anything, and probably make things worse, since you now have to insure somehow that not only the pitch/throttle is mixed correctly, and that the gryo is also working in the right direction with the proper gain. My suggestion is to start slowly, don't even take off. Put in enough throttle for the controls to start working, then master the rudder, then going from side to side, foward and back. Then you might think about hovering. Oh yes, a similator helps also.
Here are a couple of links you might find useful. The latter covers a Piccolo, but the general concepts/problems are similar.
http://pgoelz.com/
http://rchelibase.com/heli/
Good luck!