Just to murky up the waters even more, i ran a 400 lump in my '6' for 6 months over a winter, all the ancilliaries were '6' , ran fine. apart from a lower top speed, in fact i think that 400 is a sweet little engine, it revs so well (less reciprocating mass?) you hardly notice the lower power output. I wonder if anyone has tuned the 400?
Any differences in the CDi's must be pretty minor, if i had 60 quid to spare i'd take my bike up to Straight Line Racing in kings lynn and bung it on the dyno and map both CDi's,
I know some of the srx racers use magnetti/marelli or boyer units so it is probably a fairly simple curve anyway.