My suggestion is the 69 2 3/4". I have one and love it: Easy carry and good balance. While reading your question, I took my 69 and just laid it on my chest as with a chest holster. Good fit. I think a 4" might be too long unless in a shoulder holster, or the old Navy style aircrew/pilot holster. If I wanted to use a shoulder holster, I'd carry my 6 1/2" 626, ignoring the weight issue just for the example.

Also, as a suggestion, given your application, is to use Bianchi speed strips which will carry more compactly than a speed loader.

Experimenting with holsters, that 69 fits me IWB comfortably, even more comfortable than my M&P 9.