No regrets at all - the only thing I really miss is Global Blocks, but I knew that the AX8 didn't have them (with no promise of getting them) going in.
I was nervous going in after reading a few threads about people hitting the CPU threshold, as well as people using external reverb pedals to reduce CPU load, but I haven't hit those limits yet.
I have made some small adjustments, but nothing major. The main one is I've gone from two drive blocks down to one. To be honest, even though I had two drive blocks in my AFX II patches, I only ever used one. I used scene controllers to vary the amp gain or input trim to give me my various gain stages. The drive block was really just a clean boost to push the amp harder. The same thing can be achieved with Filter blocks and/or PEQ blocks which take up much less CPU.
Having everything built into the one unit is simply fantastic. I'm finding I have more flexibility compared to my AFXII + MFC setup, mainly because you can assign switches per preset and there is the push and hold for X/Y function. Maybe I didn't explore the MFC far enough, but I felt a bit restricted as you had to assign the footswitches, so even if a preset didn't have a certain effect, you wasted a footswitch as it was already pre-assigned. Similarly there may be an effect you don't use often but is called up in a certain preset, you may not have an IA assigned on the MFC but the AX8 you can do that.
