I also suggest that you look for an adjustable rear sight pistol as many different ammos place differently & with the fixed you'll be limited..
I've only had one 4" MKII & prefer the longer barrels & longer sight radius..
If your gonna shoot it, Which you should BTW, You will want an adjustable rear sight..
Also Ruger sights these pistols with a Bullseye target were there aiming lower than the point of impact, I prefer shooting dead on & will turn the rear elivation screw counter clockwise to my specs of shooting style & ammo, with the fixed sight your limited..
There are some 4" bull barrels out there with adjustable sights..
Also I prefer the MKII over the MKIII..
First the magazine won't drop out without modifications as there's a magazine disconector safety, also this makes breakdown more trouble too..
The mainspring Lock/Safety is just an add on to make liberals happy..
The loaded chamber indicators have been known to cause trouble when they get caked with rubbish, alot of people are replacing them with an aftermarket part..
I likes the look of the MKIII magazine release button but without a MKII bushing & hammer + a Volquartzen magazine ejector it isn't gonna work like a 1911..
Just some things to think about..
Many folks like the MKIIIs & have great luck with them..
Also don't overlook the 22/45 MKII/MKIIIs as they fit the hand more like a 1911 & the newer ones can be had with 1911 style wooden grips, but they have a polymer frame.
Here's my Favorite Ruger Pistol
1986 Ruger MKII Target KMK678