I also have a Futaba 4GRS, I upgraded from a CoreRC one. I wouldnt personally say it made a massive difference to my driving, but I could tell the response time was faster than the CoreRC and it does feel nicer too.
I've noticed a few of the top drivers in my area use the Futaba now too so must be half decent and quite a saving over the KO/Sanwa.
As for options, the CoreRC has pretty much everything the Futaba has, it is a pretty impressive transmitter for the price... considering just a Sanwa receiver is more than an entire CoreRC transmitter & receiver
