I recently had the same chance encounter with a M66-4 2-1/2" and even with the gut feeling that for the price they were asking online at GA ($500) that I should buy my first 2-1/2" M66 as I typically only buy 4" with the exception of 1 3" I purchased for CC. I even ran it by Forum site members and got the comments that it won't be there when you go back to buy it routine, which in most cases should have been accurate. After speaking with the seller who seemed knowledgeable and a no B.S. fellow I thought what could I loose. Well I can only tell you in retrospect it was the best online deal I have ever made as I see them for no less than $700 and upwards to a grand. Price aside I am totally dazzled by this well preserved piece, the -4 was the last variant prior to the advent of Mim parts which gives my acquisition added value. Most importantly the feel in hand is truly unique to me and I love it. The -4 came with stock Hogue grips which I will be replacing with a nice pair of Ahrend Brazilian walnut finger grooved grips when I clean it up and get a coat of wax on it. For my liking this is a bit heavy for a CC but I went out and purchased a OTW looped pancake Lobo holster I like this gun so much. Super long story made short , BUY IT NOW (if still available). I was lucky to have only debated the decision for a hour. It's true that sometimes a deal does find you the only problem I now face is I would like to own more and am finding they are almost as sought after as the 3" barrel older Smiths . Good Luck
