RE: Fins for S-Type 126
Ideal fin tuning for ST also depends (more than average) on the ride style that you're aiming for (slalom/freerace/superX etc).
In general, based on your current set up :
Light to medium powered 7.8m : 390 Drake
Powered 7.8m : Select SX 360
Underpowered 6.4m : Drake 390 (use 7.8m !)
All other 6.4m : select SX 360
5.4m : Select 360 or smaller (320 slalom or 300SuperX)
Hope that helps sort it, let us know if you need more..
Cheers ~ Ian