Re: SPD based on Active Cost
It's more relevant for supers, but at the moment, GM convention or various "rules of X" limits SPD for characters, on the basis that (generally) you shouldnt be superstrong and superfast. Seems to be a cost adjustment to make it prohibitive is better than a GM fiat, and more in-line with the Hero philosophy of 'no absolutes'.
Introducing a variable cost to SPD reflects that powerful characters get disproportionately more benefit from SPD without having a blanket limit.
I understand the point about DEF and OFF = Effectiveness, but this is a prior step. Possibly E(DEF) and E(OFF) = Effectiveness, where E(OFF) = OFF x SPD.