38mph just from the cdi cut is very good, think I only got to about 33-34 max when I did mine.
Yeah, in general,
Lighter rollers = better acceleration, slight loss of top end speed.
Heavier rollers = slower acceleration, slight gain in top speed.
I fitted 5.5g rollers, cut cdi, smoothed boss, race variator, #82 main jet, iridium spark plug and got about 45-48mph showing on the speedo generally driving on the flats, now and again it goes just over the 50mph marker down hills.
Since then I fitted a 1000rpm torque spring and this helps goin uphill, gave me an extra 5-8mph up hills compared with stock torque spring. Keeps you in a lower gearing longer and you feel more torque in the engine. Also going to swap my fly springs in the clutch for 1500rpm springs, that gives better off the line speed by letting the engine rev higher before the clutch grabs. Just waiting for them coming feom taipai.
I still have my stock exhaust and airbox right now too, plan to upgrade these one I get the cash tho, just cos I prefer the look, I may gain a couple of mph top end too tho if im lucky.
I would do the boss and main jet 1st and see how you feel with that. If you want to you can then fit a race variator and move onto the torque spring and clutch spring later if you want to go that far. I dont plan on changing my cc, on mine, prob just go for a bigger bike next year or 2.