I'd guess 4000rpm would put the speed at the edge of the bar pretty high! Might genuinely put the second layer of HDPE on HardWired just to be sure in that case...

As for speed though, it's not that big of an issue really since you're protected across all sides by the great big spinning bar on top, so it's not like you need to outmanoeuvre anything, unless your bar stops spinning for whatever reason. I'd assume that the smaller wheels put pushing power up though, so it's like you say really - swings and roundabouts.