Samuel,
This choice you are contemplating has a simple solution. Since you already have a M-19 and are so fond of it get the 2-1/2 incher to keep it company.
OTOH, you might find that the 2-1/2 incher is too short to balance correctly in your hands. If that happens, then get the three inch M13/65.
Then get ready cuz there are some 3 inch M-66s out there and if ya stumble onto one of those... get it!
Then get ready again, cuz what with that 3 inch M-13 you already done got, you'll absolutely NEED a 3 inch M10 to go with it! Heck, when you get that M-10 in 3 inch, RB, that may just be your final K-frame gun you'll ever want.
Except maybe for a K-22 and a K-38, you'll NEED a minimum of one each of those. But then that is a different subject all together, isn't it?