I have found that as the idle current lowers from class A towards class B, at some point the sound will start to be perceived as leaner.
With that said, class AB is not a problem if one biases towards descent values, not close to class B.
From .45 to .43 is most likely a couple of ma, and is not going to make any difference in longevity. However, I would check the sonics and see if .5 or higher would be perceived differently with the KT-88s. Set for the best sound. (Always be sure the power tranny does not overheat.)