jsl ... Welcome to the forum ... Glad to have you aboard! While we may be a bit biased here regarding the MK Series pistols ... it is with good reason, as the MK Series pistols are consistanly among the best when it comes to accuracy and durability. While my personal favorite is the MKIII512 (in terms of overall grip angle, balance & accuracy), I would recommend that you:
1. Handle as many different versions as possible to determine what feels best in your hands.
2. Rent and fire a MKIII as well as the 22/45 for comparison before you make your decision.
If it ultimately comes down to the weight issue for you, you may want to consider the new 22/45 with replaceable grips as it is a 5-1/2" bull barrel model, but only 33 oz. http://www.ruger.com/products/2245Re...ls/models.html
Good luck with your decision.