Congratulation on new baby and you will love her with Manual Transmission.
We had long discussion with you through several threads and I'm not gonna start it again but to me M-DCT is one of the best Dual Clutch transmission in the world period. It's fast and amazing. Maybe the only minor issue with DCT is the very short first gear with 4.8:1 gear ratio... maybe something like 4.1:1 (that is the 1st gear ratio in MT) would improve the launch significantly. Still I miss DCT however I am totally in love with this BMW Manual transmission with completely right gear ratios.
As far as size I believe the current M5 is a little big. Maybe 3-4" shorter was the great size but wait the next generation will be even bigger...
Anyways, don't forget to post some pictures of your car