Wow, every answer under the sun.
Have you tried the 22/45 that you were thinking about? You said you didn't like the MkII grip, but the 22/45 is very different. I don't remember what mine cost, but it was around $250 NIB. You can get better sights/Tasco Optima for another $120.
For me the Ruger 22/45 is the right choice. My semi-bull kmk II goes to my more powerfully built bro-in-law if his sorry ass ever returns to stateside.
From the Buckmark and the SIG, it sounds like you have better feelings about the SIG, and unless you have kids to feed or other pressing financial commitments, do yourself a favor:
always get what you want the first time