don't let HP fool you, most riding is all about torque, the 4 valvers knock out about 10% more and that's what they feel like.
The S4R sounds good!
well, you can't make horsepower without torque, and it's torque that drives you off a turn, but that feeling you get as your speed builds, as your revs rise in a seemingly endless surge right to the redline, that's horsepower, and it's adiictive. Real V-twin horsepower is intoxicating, gixxers, blades, R1's, they have a bigger top end rush but it's all at the top end, they feel like a 600 till the fuse burns down but it's inaccessible most of the time. V-Twins, 4 valve ducati's especially, make serious torque and therefore, serious horsepower everywhere.
Not sure if you're 10% difference is accurate or not, though i doubt it, but the real difference is how fast the 4 valve engine makes power, they accelerate a lot faster because they rev a lot faster and the gains made on every gear change add up to a LOT more than a 10% difference, anywhere.
i love my radiator
i love my hoses
i love all that other crap!
paul.
p.s, yes, the S4R sounds good!