just remember, you're not used to this kind of speeds anymore,as before.
risk factor is more then double.
sort of ask yourself : on wich bike do you see yourself ride the longest (without getting injured,or loose your licence).
i also have the Z and think about trading in for a twin (-allroad), but the only advantage is riding faster and maybe just a tad smoother engine.
so where's the win on a faster bike?
an idea is to rent a faster bike from time to time and keep "the good one"?

think hard before you abandon ship ;-)