I'm not a serious bicyclist, but I have owned a Windcheetah and I currently have a recumbent bike. You feel the difference in power when going up hills because you can't stand up on the pedals but just have to gear down and spin. The other difference I noticed is that recumbent bikes put a lot more stress on the knee joints when pushing hard because your held in place against the back of the seat. I used to ride my recumbent 13 miles to work 4 days a week but it is all uphill on the way there and I found my knees unable to take the abuse day after day.
I owned a full bodied Windcheetah for a while. I took the body off because it was inconvenient for everyday riding. I sold it after a short period because, since I do almost all my riding on city streets, it was very dangerous. It was so low that you can't be seen alongside a car. In addition when approaching an intersection, the rider is looking at car fenders and not thru car windows to gauge approaching traffic. The purchaser was in NYC which I thought indicated a death wish.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13