I am with you on that... although, as when I tested (1.27.something) the max attack rate was 10/second.
The maximum base attack rate is 10 per second. However with +400% faster attack speed units can shoot up to ~45.5 (45.45?) attacks per second which is the absolute maximum standard attack speed.
This limit should be reached with just 354.55% faster attack speed, however it appears that the full 400% is needed otherwise it will shoot slightly slower at around 45 attacks per second. At such insane attack rates it seems the last ~50% of faster attack speed make extremely little difference, pointing towards there being attack speed break points. Also the fact it does not reach 50 attacks per second points towards 400% faster attack speed being too little to reach the required break point.
Using the new trigger actions to set unit attack speed the new absolute maximum possible attack speed is exactly 50 shots per second. Faster attack speed no longer makes a difference. This attack speed is not achieved at 0.02 interval like one would expect but rather at a significantly lower interval like 0.01 again hinting at there being attack speed break points involved.
50 shots per second is a strange number. It might be related to PAL frames, but could also be because a technical interval of 0.02 should achieve it, but does not due to rounding error.
Attack speed set by triggers will be effected by faster attack speed. Hence one could make a unit have 20 attacks per second at 0% faster attack speed and still shoot faster when gaining faster attack speed. The hard limit of 50 attacks per second will still apply and with rounding error even 400% faster attack speed might not suffice to reach the 50 attack per second break point.
Hmmm... is it possible that the attacks also have a limit like movement per player ? :|
There is no such limit as far as I am aware, I was easily able to get 22 units to perform ~1,000 attacks per second.