Running outdoors I would recommend you getting 48Pitch gears, such as kimbrough, the 64 pitch will not last. try say 76T, 77T spur and a 13T, 15T pinion in 48 Pitch for starters...
I run the same setup in my Lajf Racing widened X10, and we run 4T motor 2cell Lipo with a 55meter straight.
Xray T4-14 (BLS551,4.5T/8.5T, Spectrum), Xray X10-15 (Lajf Racing widened 235 4T, IRS)
Lajf Racing P28(LiPo, spectrum), Lajf Racing P28GT (LiPo, spectrum )
Xray X1(21,5T, spectrum) Tamiya M05(tamiya ESC, silver can, spectrum)
Go 235mm with X10 widening parts from www.lajf.se Get your P28 at www.lajf.se/pshop