An update for anyone that cares.
I feel like 18 rps is normal out of a CYMA 106 platinum upgraded on 7.4v.
Made a deans converter for fancy 11.1v RC plane battery and tested it again. Pretty sure up to a point, current plays a bigger role in rate of fire than voltage.
Now, my chrono might be bugged (hope not its brand new), but I was getting around 52 rps 😬 The fewest amount of bbs I could shoot in full auto on one tap was 5!
This was with an Overlander batteries 3 cell, 11.1v, 1350mAh, 95C burst - 50C constant battery. So can deliver 128 amps or around 1.4KW on burst.
Built the 106 into a PCC with a longer barrel and softer spring and its now shooting at 22rps at 315 fps on a 7.4v. Was at 335fps with everything stock.
Just for fun I tried it again with the RC battery in the PCC setup and I saw 64rps!
So the AEG is fine and anyone who wants a BB hose should get some fancy batteries!