I'm looking at a Vermeer RT650 trencher right now, and wanted your opinions on these machines. Reason for purchase is to do small acreage farm drainage (1-15 acres most likely). Most of the tiling is 4" at approx 24-30" depths. I've found some in the 20-30k range, which seems reasonable. I'm wondering how many feet per minute these could do at average 30" depth in clay-loam soil - I know their are many variables, but even a ball park idea would be great.