I think it's a little borderline whether you could freeze motion of this type using 500Rs. They have a duration at around 1/900th second so faster movement during your shot will result in a little blur.
We have a mixture of these and the 500PRO heads (the pros are 1/2500th sec) and these freeze most things. I also know of a studio that specialises in high end dance photography who have found their Bowens Quads (I forget the exact speed but its something like 1/4000th of a second) is still not enough for them, so they're going for a rather expensive Bron pack, which is something crazy like 1/20000 second duration.
Going back to the o/p, have a try with a couple of speedlites too, as these offer ludicrously fast durations at middle to lower powers, so a few of those could be a decent solution if you did the Bowens are too slow for you.
I think most manufacturers quote t0.5 times, including Lencarta for their standard range.
Bron quote t0.1 times, and Lencarta's new "Super Fast" range claim a range of around 800th second at full power rising to 10,000th second or 20,000th second at full power depending on it's the 300 or 600 w/s head you're using.
From memory I think my Canon 580EX at 1/128th power has speeds similar to that too
Was slightly wrong on the times for PRO's - they're 2,900th sec (t0.5) which would equate to approx 1,000th second t0.1 by the way.