Homebrew PCBs

I've been working on mechanical etching of PCBs using V-bits from 
Think & tinker (http://www.thinktink.com/) and having some great 
success. I just uploaded two pics to the Ghidera2000 photo album 
(pending approval) that show 0.010 traces cut with a 45 degree bit. 
One is an actual board I'm using and the other was a test of SOP and 
QFP packages. The camera won't focus up close and I'm no photographer 
so they're somewhat blurry. Some parts look like the trace was rubbed 
out and others like there is no cut, but both metered perfectly, no 
shorts etc.

Anyway, this is working so well that I want to try out a 0.005" stub 
endmill but I'm uncertain about the feed speed to use. I'm hoping 
someone here has experience with very small bits. These things are 
over $30 each and I ain't rich 8(

Anyway, the IPT for hard copper with a 1/4 endmill is about 0.006" so 
a little proportional math would have the IPT at approx .006/.25 = 
0.024% of the tool diameter. For the 0.005" bit that makes 0.00012" 
IPT. I'm assuming hard copper because I really don't know what type 
is used on copper clad boards.

My spindle runs at 24,000 RPM so 24,000 RPM x 2 flutes x 0.00012 IPT 
gives 5.76 IPM feed speed max.

Does this sound correct?