To be honest you don't need to change the gears to metal, so long as the slipper clutch is set up correctly you shouldn't have any problems.
The 35 is a bit slower than the 27, but it does have more torque.
I can't comment on which is the better transmitter as I have a spektrum 2 channel, it's all I need.
I would take it out and run it, see what you like about it and then change what you don't like, no point spending a load of cash just for the sake of it.