Agreed. I'm using VFDs on two machines at home already, a 16" South Bend metal lathe (3hp) and a Baldor pedestal buffer (1.5hp). A 5hp (~4kW) VFD won't be cheap, but variable speed would be a nice feature for sure. Overclocking older motors which aren't "VFD rated" isn't something a motor manufacturer would ever recommend, but there are countless examples of people doing exactly that in short spurts with no noticeable impact to the motor's life. BTW, the same thing applies to underclocking...for motors relying on shaft-mounted fans for cooling, running too slow is worse than running too fast.