Nebula more so than Acquas. The late core Acquas can be pushed pretty hard. With Nebulas its best to start with the -18 and then play around to find the sweet spot of a sound.

Regarding cpu its a case by case bassis. For example they were getting pressed for improving meters so when they started modifying this the cpu took a hit. The new Emerald seems to be pretty cpu light comparitively so they might be moving in the right direction.