I don't think you guys are going far enough, it's not just about your equity vs the opponent's 3bet continuation range or your equity vs the opponent's Cbet continuation range but what board textures you want to represent and what lines of play you want to construct post-flop, because having a hand like 75s will lead you to representing more low boards (742)(6)(5) and barreling more aggressively while having a hand like Q2s will lead you to representing more turned scare cards 742(Q) and give you the ability to include more potential lines of play i.e. you can check/call Q8s on Q72r with a reasonable expectation of show down but you can't check/call 75s there at all. You'll also find your opponent's responsding to your turn barrels much differently on 742(Q) than you will on 742(6) by playing back at the over card more aggressively by shoving his floats, where having the additional bluff catchers (and no, not all bluff catchers are made equal) come into play.
I don't find the SPR argument against SCs to be convincing, because regardless of the SPR the number of bets, 1/2 1/2 AI, and the commitment threshold in a 3bet pot is usually the same as in a raised pot unless the villain is shoving flops in a 3bet pot or min-raising turns in a single raised pot, and in some ways it's beneficial because you're OOP and you're able to close the action with a hand that wants to do so (check/raise shoving gut shots on the flop, overbet shoving combo draws on the turn, shoving the river etc). It's only when the SPR reduces the number of PSBs for SCs to 2 that I totally disregard them in my 3bet bluffing range, which is why I think we can all agree that Q2s is clearly > 75s when you squeeze.
In the end, it's not THAT big of a deal, and I personally find myself 3betting SCs in ring games and Kxs, Qxs in HU games for my own specific reasons, but you guys really need to stop quibbling about a few points of pre-flop equity and SPR like that shit actually means anything and THINK about what you're doing and why on a more contextual level.
Eidt: If opponent's 4bet/fold vs 3bets, hands with blockers are always better than hands without, which should A) obviously lead us to 3betting Ax and Kx in position and B) by extrapulation lead us to calling 3bets OOP when we know his range construction and can guarantee ATs, KJs has more equity vs the bottom of your villains 3betting range OOP than it does IP.