Hmmmm, just found some info regarding the YZF-R6 COP's (Coil On Plug) and it looks like you are correct about a lower resistance producing a larger spark.
Be very careful with the COPs - the '99-05 models (and '06+ 'S' models) were CDI, and use low-resistance (~ 0.2-0.3 ohm) coils. The '06+ are TCI like the FZRs, and have high resistance (~ 2 ohm) coils. The risk with using the wrong coil is too low resistance = too high current = dead ignitor box.
Taken from here:- http://www.fzrarchives.com/ipb/lofiversion...php?t45254.html