I'd say try raising the tyre pressure of the R2's to compensate for the temperature. You'll lose a bit of grip (but gain a bit of responsiveness), but less than a change to R3's. If that doesn't work, you might find softer R3's work (to get them up to temp a bit more) but at the expense of making the car feel all soft and mushy to steering inputs.
Trial, error and lots of testing are the ways to find out.
I'd try my damnedest to stick with R2's myself.