It's interesting to note that the Merlin 46 power curve is very close to that of the Merlin XX series in FS gear, per the Merlin 22 power chart.
Given the 9.49:1 gear drive ratio and 10.25" impeller diameter of the Merlin XX supercharger, tip speeds at 3000 RPM are 1273.294 ft/s.
And on Merlin 46, 9.089:1 drive, 10.85" impeller, so at 3000 RPM tip speeds are 1290.876 ft/s. So only slightly higher, and apparently achieving very similar mass flow and pressure ratio (and efficiency) given the critical altitude for given boost pressure and the given power at altitude.
Also, it seems like running higher boost levels at 2850 RPM would've been a reasonable workaround for the problems the RAAF had (and presumably other tropical operations with the Merlin 46) given charge heating should've been similar to the Merlin 45 at 3000 RPM (or just slightly higher), with a critical altitude of around 7500 ft for +16 PSI and around 1470 to 1515 hp. (1515 is about right with a straight line continued from the +9 PSI 2850 RPM curve, but assuming a similar lower altitude curve to the 45 at 3000 RPM, then a 45 hp loss at 7500 ft would be close to correct) The Merlin 46 at 2850 RPM should cross the Merlin 45 3000 RPM line at just above 8500 ft, and have more power below that. (Merlin 46 should be ~1455 hp 2850 rpm wide-open throttle at 8500 ft, vs 1450 hp 3000 RPM +16 PSI boost part-throttle for Merlin 45)
For climbing conditions, they'd still be limited to 2850 RPM +9 PSI if they were already overheating/detonating at those levels, unless they dropped to lower RPM to further reduce charge heating. If the Merlin 45 was tolerating 3000 RPM +9 PSI climb conditions, then +12 PSI at 2650 RPM should've worked for the 46. Likewise, if the 45 tolerated 2850 RPM at +12 PSI, the 46 should have been OK at 2650 RPM at +14 PSI.
You could mess around with other RPM and boost levels, but sticking to the existing max continuous and 30 minute climb limit RPMs would mean only modifying one variable (boost pressure) compared to established standard operating conditions.