the difference is noticeable, your t5's will hold you back with the cub cylinders tho. the difference with stock or 4mm serval price wise is around $500 (Crank, bearings, seals and gaskets) the 4mm will push a bit more hp and tq (torque being very noticeable over the stock cylinder) and for around 550 bux, i think its worth it.
if you go stock stroke, there will be less bike down time and youll be back on the sand in no time. if you go 4mm, youll have more hp and tq and will never have the thought of " should have i gone 4mm ? "
i dont believe it would be worth it, running the t5's.