I managed 356.3 @ a rolling road day and still have the top mount.It is more relative to engine set up and boost preassure that will make the job easier or harder for the cooler to do a good job.
If you are running excessive boost preassure then this will put an increase on the inlet temp ,in turn dropping the potential power. By running a concervative amount of boost with proper engine and management set up there is no reason that you should not be able to keep the stock cooler.Most people just spend money on various upgrades and never spend nearly enough on set ups.