If you can find a new SV frame, send it to Bob @ Brazos and I'm sure he will build the ProSX with it. That's what he told me last time.
I really don't know too much about IMM, but I do know few things about Brazos guns. Bob spend time talking with the shooters. My girlfriend has hands that are much smaller even than average female. Bob traced her hand, and cut the frame to fit her hands. She shot quite a few different STI/SV from various builders in the past few years, and the ProSX is still by far her favorite gun. I remember Bob talked about MOA size of CMore, and he helped me to make the decision based on the age of my eyes, typical distance we shoot here, how fast I could find the dot, and also the number of sunny days based on my geographical location.
Although most ProSX look the same there are some minor differences including where the gun is lightened externally and internally. Combines with individual shooter's ability and other parts used that's how Bob get the balance right for each shooter. Bob also put in A LOT of efforts into his "Pro Tuned" parts. I don't know enough to talk about the details but I can tell you they work better than 99.9% of the parts I tried in a 2011 platform.
I think the best thing to do (as everyone already mentioned) will be calling Bob and/or Brandon and discuss what you want to build. I'm sure you'll be happy with guns build by either one, but Bob was my choice. And I'm 100% happy with that decision.