Because you mentioned installations, I want to mention something here that I haven't seen on the BBS. And to render it down.... "The sequence in which to install programs is crucial". If you are going to install both, do 8.5 first. It may be obvious, but there, I said it. This applies to PC's in general, plan the install sequence.
One notable plugin that I miss that is in 8.5 but not X3 is BEATSCAPE. I would miss that as the defunct replacement appears to the MATRIX. Someone can correct me if I'm wrong. Specifically, BEATSCAPE had the AKAI 16 pad layout, but it had adjustable parameters for each pad, even with effects. Not to mentioned the segmentation screen on the bottom half. Still a great product!