Well, by virtue of the higher areal density of the platters, the performance will inherently increase especially during sequential transfers. So, the newer drives will benchmark a little faster.
I really don’t see 1.8” gaining faster RPMs until they become more mainstream. You figure that that these drives are designed for low power operation and not mainstream performance. A majority of these drives aren’t actually being used inside computers but rather portable audio/video players instead where high RPMs are a waste of power.
Perhaps as devices continue to shrink and if Toshiba gets any real competition in the space there will be more advances but for right now 2.5” seems to be the current battleground.