Actually, last Friday, I did an empty house, about ~3500 s.f. It took me like 6 hrs from the time I came in and left the house. At that time, I wanted to use a bigger and faster machine. Plus I want the 20" to be used for commercial jobs.

3500 s.f. is a pretty big house. I hope you charged them at least .20/s.f. If so, then you made $700, which is about $115 per hour. But unless your area is very different from mine, you won't get too many 3500 s.f. residential jobs. If you are going to invest in additional equipment for moving more quickly thru your larger jobs, I still advise either the Challenger Titan 17 or the Orbitec Defender 17.