R44 ROD in Auto at 60kts is less than 1800fpm. The published figure of 4.7:1 can be achieved when using the max. range configuration (90%RRPM/90kts)
At 90kts (= 9,100ft/min) forward speed, you would get 4.7:1 at a descent rate of just under 2,000fpm.
I would imagine the low-rpm horn would be going off.
Yes. Minimum allowable RRPM in autorotation is 90% though, so you are within limits.