I tried QV3MERC, but my Prodisc S03 burn speed seems to have dropped from 12X with Milestone Version 2 Extreme all the way back to stock 4X with QV3MERC. One is left to wonder if this is deliberate?
I tried reading the Extreme V3.txt file that accompanied the firmware, but all it told me was the following:
PRODISC S03 -> Linked to MCC01RG20
You page http://freeweb.siol.net/tvajng/Quikee_FW.html details all of the speed limitations, but it's difficult to determine this information from the Extreme V3.txt file.
I suspect that all of this was detailed in the documentation that accompanies the patcher, but unfortunately, I do not have access to it.