Hi,
The 'roid spawn rate caps at 1/sec but their velocities never cap and pick up with each new Wave (every 10 spawns).
It gets noticeable for me ~W15 and pretty much unbeatable ~W30-35 while the gun rotation rate never changes.
Maybe shorter Waves are in order? Every 5 'roids, say?
Thanks for the comment and thanks for playing :)