I buckled and purchased the 365X slide with the RomeoZero. Impressive little package. Having the original slide gives good reference on where to cut the RMR clearance into existing holsters. Overall I am very pleased with the new sight and am landing tighter groups than my not-so-young-anymore eyes have made in a while. It is still an extremely tiny package and hides very well.
Also. Here is the best 2d size comparison available.