A buddy bought a Speed-Six when they came out , I have a model 66 S&W , we shot both extensively , side by side. The Ruger is a tiny bit heftier , not by much but it is heavier a bit, just enough to be noticeable.
The S&W K frames are still the sleekest designs in the 38/357. To me Ruger's have always been beefier , but sometimes that's not a bad thing!
Gary