Delivery time will be the same either way.
There will be no power difference. We upgraded the power supply in the C revision, but this was more for long-term reliability* than anything as power output was, at best, marginally increased - I expect people to be using these years from now
The difference for the D revision is the MASSIVE crossover update.
* - There were no problems with amps with the 50-amp FETs, but I am a fan of over-building things.