That's not fast. I resurface my waste board using a 1 inch cutter at 120 inches per minute / .01 depth of cut / 50% step over / plunge at 40 inches per minute / Dewalt DWP 611 speed dial at 4.
With a new waste board I actually use the same specs as above but adjust the feed rate to 150 and depth to .005. Before I start cutting I probe around for the highest spot and zero to that. Then I take a pencil and draw a bunch of zig zag lines to use a reference when milling it. If all the lines don't get milled away on the first pass I re zero to the high spot and run it again. I repeat until all the pencil marks are gone and will have removed as little material as possible.
If you have to remove .0625 to get it flat then you should look at the height of your Y axis rails in relation to the waste board. Make a spacer that fits perfectly under one end of one rail. Then loosen all the screws that hold the Y rail to the endplate and lower or raise the rail to fit the spacer height. Then move to the other end and repeat. Switch to the other side and do the same. The Spacer should slide down the length of the rail without any increase or reduction in the gap. If there is then you need to look at leveling the base of your machine. (Make sure it is flat and true with no high or low spots. If there are then shims can help.)
If I have some deep grooves to remove I increase the depth of cut but do not lower any of the other settings. I would not cut much more than .03 at one time. With proper carving and zeroing of the Z axis you shouldn't have any groves to remove that are much deeper than .005
Why remove any more of the surface than necessary. I prefer to preserve mine as long as possible.
Of course this is jut my 2 cents worth but it works very well for me and is a quick cleanup of my waste board when needed.