| I have a 748S, I use Diablo Corsas on mine. 4000 miles on a rear, more or less double that on the front.
So it sounds like yours are about ready for a change. If the front feels like that, then probably best to change both. Bit more money, but always feels so much better.
I used Bridgestones on my old R6, they seemed to be ok, but somehow the Pirellis feel a bit more stable. Mind you, that could be the bike! | 
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