A good set of plug leads will make no difference compared to top class racing leads. The top class stuff allows a fatter spark, but once there is enough to ignite the fuel there is no need for any more - fuel is now burning so any more spark can't do anything more.
If you look at today's top sports bikes they are getting 120+ bhp from 600cc at up to 18000 revs. They use the same plug lead tech as cars and most of them use wasted spark systems.
Stick with something simple like Bosch and spend the money on more effective upgrades.