Another approach is to use perf data for PACKS ON (assuming you're not TOGW limited), but select PACKS OFF to reduce EGT/TIT a few degrees. In the long run it's good for engine life.
I'm interested in the RR periodic PACKS ON TO check for stall. Other engines (CF6-50 comes to mind) used to have an "off-idle hangup" (actually a low-energy stall) if packs were off at throttle advance from ground idle. It could be cleared by turning packs on, then off again at half-throttle.