The 4" SP101 is a good choice with that extra 1" of barrel and a little more weight to mitigate recoil without being too heavy.
But based on my experience be very, very careful getting one made anytime in the last 6-8 years. Won't bore anyone with the long version of the story but I went through four SP101’s – two of the 4” models and two of the 3” Lipsey’s models with adjustable sights, and all of them were QC disasters. Sent them all back, Ruger scrapped two as being irreparable and finally gave me my money back on the fourth.
Took a chance and bought another 4” model (my 5th SP101 of recent manufacture) after examining it. Still had to firelap the rough barrel and redo the crown on that before it shot okay but now that I have one whose barrel comes straight out of the frame and shoots well I really like it.
Decently made SP101's are certainly out there and would be a good fit for what you want but I would strongly recommend not buying one sight unseen if it was made anytime after about 2014 or so and the more after the more careful you should be.
OR - just get one of those 3" Model 60's and have fun.
