Thanks.
Moved an EoTech 516 I had on my PS90 to the M4 rail today and it seems solid. Cnx'd my order for the XPS sight and bought a T-1 on a LaRue mount to install on the FN.
Beginning to think no carrier on the weapon itself is all that important. As a home defense weapon, 6 or 8 rds is enough, and if you need to bug out, a bandolier is probably the best approach.
If and when somebody makes a good picatinney rail for the M4 I'll buy it.