This is an interesting thread and since I own the same gun (7.5" RH) I thought I'd take a closer look at exactly what I'm getting as compared to the OPs numbers and perhaps we'll be able to see some correlation here. I've always been aware of my higher than expected velocities from my RH and was blissfully ignorant that it could even be a potential problem. Like the OP, I've never had sticky extraction from my RH or anything beyond a little flattening of the primers. Considering the test barrel length of 4", I still don't think there's a problem, but there are greater minds than I so I'll throw this data out there for your perusal.
Some of my loads vs book velocities are shown. My Lyman #48 shows a 4" test barrel. Book velocities are shown in parenthesis ().
245 gr Keith (Lyman #429421)
17.0 1209 FPS (below book startload of 18.5gr for 1087fps)
18.0 1274 FPS (see above)
19.0 1287 FPS (book max is 20.6gr for 1248 FPS)
24.0 1448 FPS (1218 FPS)
8.0 953 FPS (below book startload of 9.8 for 912 FPS)
255 gr SWCGC (Lee. Very similar to Lyman 429244 in book)
21.8 1377 FPS (1097 FPS)
22.0 1417 FPS (max is 22.8 for 1186 FPS)
I have other data, but for other guns, boolits and such so did not list those. I get even higher velocities with some of these loads in my SBH!.