I have an 873 and am renting an LT313 to do some trenching. Probably be going about 3 1/2 feet deep. No rocks or tree roots to go through, just an old farm field where we are building. My machine does not have hi flow, just regular. How long should I allow/budget myself to be able to do this job? About how many feet per hour can a person trench with this set up at 3 1/2 feet? Thanks, keith