Something Ryan didn't mention was pumping losses, which increase at an increasing rate with engine rpm, so efficiency suffers.

Different engine designs have different sweet spots. My V85 is perfectly happy at 3000rpm around town, but it only revs to 8000 or so. My FZ6 wouldn't really be happy at anything under about 5000rpm, but redlined at 14.5k.

You just have to get used to the engine you have and have some mechanical sympathy: don't lug it, but you don't need to rev the tits off it either.