I have a pr of 28mm flatslides with some tricks (29.25 bore with atomization swirl grooves) that I made myself. I run a low and high end motor. I dont really drag but do a cross of mx, gncc, and TT. Im debating on weither or not I should stick with these or get some 34`s. I like knowing I have a good low end flow velocity, but I think I might still gain more with a 34mm. I have RZ 12port cylinders matched to rockets, 4mm stroker, pods, displacing 385cc`s. Seems to me like it might be to much, but I have sen alot of people using 34-35mm with similar mods or even slightly less.
Also of course it shouldnt be a matter as of yet, but of course it will be rising in displacement, and once maxed, 68mm sleeved will be goin in.