Do you have any ideas on how you'd manipulate the slew rate of an IC? I don't know enough about it to chime in, but I'd assume that there's not too much that can't be done when it come to a circuit. I mean, we can even do digital to simulate various distortions and amp models now, right?Yeah, current Rats use the OP07. If I were a company building Rats in large numbers, I wouldn't want to have to deal with supply issues with sourcing 308s. Maybe there's enough of them out there for a niche builder to produce them for years to come, but I personally wouldn't tool up if I built them by the tens or hundreds of thousands.
Also, the specs for the OP07 and 308 are the same, at least where it should matter, which is the slew rate. Since no one has done an actual real double blind test (TTBOMK), I don't think it can objectively be concluded that the 308 does indeed sound better. And if it really is a matter of different slew rate between the two, you can actually adjust that, by increasing/decreasing the compensation cap.
...I wouldn't be surprised if most of us who swear a 308 sounds better aren't actually just fooling ourselves. This is possibly especially true if someone is trying out the latest Rat 2, because ProCo has made at least one component substitution that makes them sound audibly different.