[dkhm3]

I don't own an M5, but I had the same zf8 on my X5M for 3 years, as well as experience with PDK and the DCT with my 911 and my M3.
I consider the goal of any transmission to be:
1. fun to drive manually
2. to be in the gear you desire when you desire it as quickly as possible.

Considering this, the zf8 has been one of the reasons I disliked my driving experience with the X5M.

Perhaps they have made some improvements on the zf programming, so I may be wrong but here is my evaluation of the zf8:

+
shifts as fast or is actually faster than the dct on 1 gear changes
works much better in auto mode vs DCT, on parity with the PDK

-
Does not down shift multi gear requests very well: example- if you are in 7th and want to go to 5th, the zf will go to 6th then 5th. if you are in 7th and want to go in 4th, it will go 7-6-4, skipping 5th. Both PDK and DCT skip immediately, 2,3, gears etc.

Abrupt downshifts- DCT and PDK will downshift immediately and smoothly, while the zf will jolt on downshifts at high RPMs. DCT/PDK will snap gears on upshifts which is much more satisfactory at WOT, the zf will not.

Overheat- prolonged very aggressive manual shifting has over heated my x5m 3 times, I have never had this on PDK or DCT.

Overall, the dct/pdk has been great imitating a manual gearbox, because it is. The zf does its best, but is not as satisfying to drive.