Shooting the Mamiya RZ67 handheld: how much sharpness one sacrifices (over a tripod and mirror lock-up)?

Setup: Mamiya RZ67 ProIID, 110mm f/2.8 lens, Kodak Portra 160NC; focusing via the waist-level finder loupe; scanned with the Nikon Coolscan 9000 at 4000 dpi (no infrared cleaning).

Scene (click images to open larger versions in a new window):

Comparison #1: handheld vs tripod, f/5.6 at 1/125s, using optimal technique (breath holding, tripping the shutter with gentle pressure) but nothing out of the ordinary… More