I have Datas on my Indoor FK and rode the SL for a while on my SubPop. They feel similar, but the SL's are a little more tweakable, softer highback, and the Datas are little more plushy. The SL's are also lighter. Lighter and a little softer for tweaks is why I say for a 50/50 split to aim for the SL's.
Though this may seem a little off topic, what model/year boots do you have?
Go ahead, drink that kool-aid.
FS: Forum Sauce 142 $200 plus shipping
FS: Flux SE30 $75 plus shipping