One other aspect of the '10 minute TO' is that many engines have a higher EGT redline for TO than for Max Con - and that's programed into EICAS (or whatever system displays EGT on non-Boeing). So at the end of 5 minutes, there is the chance your EGT could turn red if you don't have the 10 minute TO option.
BTW, if memory serves, on the 747-8 we made 10 minute TO baseline, not an option.