Yes - I can understand that at the speeds you are talking about, Mach2 implementation of backlash could be troublesome. I can see that,however, the axis must come to a complete stop before backlash can be applied, since, as I said , whether the steps are backlash steps or movement steps, the first shall we say 600 of these (1/1000th of an inch on my old lathe) will not produce any movement on the axis, they merely take up the backlash.
There is a speed box on the backlash page, and you could only shove this up to 100%, but yes, on reflection, I think the backlash pulses will be applied seperately. It may not be the backlash speed that is the problem.At 7000 rpm and a 0.006 per rev rate, your feedrate is 42 inches per minute. I don't know how many pulses per inch your motors are tuned to , so I can't calculate the pulse rate, but it might be that your setting of feed per rev (whilst it gives a good cutting speed) may be giving you the slow backlash rate, since, even set at 100%, it will still keep to the speed at which it is set (i.e. it doesn't revert to your maximum G0 rate).
I don't know what you are cutting, or what the reason is for choosing a feed rate per rev, but perhaps if you used feed rate per min, and backlash at 100% the results might be more acceptable.