You'll get a much more accurate picture by using actual loads than trying to shortcut the calculator.
Realize also that the same bullet in the 308 can be loaded to much higher pressure and so faster velocity than the 30-30, and that increses the recoil. So the closer the velocity in the comparison, the closer the comparison.
Some actual numbers from actual loads...
308 w/Win748
150 gr bullet
2540 mv
43.0 gr powder
5.5# firearm (Encore)
17.62 recoil energy in (ft/lbs)
Load Two - 30-30 w/Win748
150 gr bullet
2310 mv
34.5 gr powder
4.5# firearm (Contender)
16.53 recoil energy in (ft/lbs)
Change to some proven loads for each with H4895, same bullet but with almost 20 more grains of powder for the 308 load and so a big difference in velocity, and the recoil numbers change to 22.42 for the 308 and only 9.08 for the 30-30. Now the 308 has more than twice the recoil of the 30-30.
Bottom line IMO is that in real life the 308 will have more recoil than the 30-30 more often than not on the TC pistols just because of the loads that will normally be shot in it.
Still comes down to what you can tolerate. My regular loads in my 375JDJ's pushed 44 pounds of recoil on my Contenders, and to me they were pussy cats to shoot. My 416 Rigby Encore on the other hand started getting nasty after only a few shots fired, but it thumped you with well over 80 pounds of recoil.
YMMV