Is Wadia 860 much better than the 850?

No, not sonically in most situations. The exception is when you are using it directly into your poweramp without a preamp, and you need to be able use a balance control. The 860 has a balance control. I find that few CDs need balance tweeking, but some old CDs or those of historical performance might. If this is the case, and you need the balance control, get the 860. Otherwise don't bother, IMHO.

Yes the 860X and 861 are more resolving than the 850. Vtin asked about the 860 so I tried to answer the specific question. I shared my experience with the 850/860; at the time I made my purchase decision I could not countenance the delta in price based on the audition. The advice to listen makes consummate sense - for example, I found that a truly balanced setup with the 850 made a compelling difference over (either player) s/e. This is a factor Vtin may want to take into account. Listen with your own ears - it's a great hobby!