A Gravely Promaster 300 (outfront riding mower) with 20 HP Kohler and 60" deck with hydraulic lift with 497 hours is being offered at $3900. I am told it is a 2000 model. Is 20 HP underpowered for 60" mower deck? Was this machine significantly re-designed in later models to address any big problems? Any ideas on what a good value would be?