I had the Green 1700 from Lowes for a little while. I was disappointed with it and returned it after about a week.
I then moved to the Cleanforce 1800 and its okay, but also not enough. It has more GPM and PSI than the Green, but still pretty weak.
I now (maybe 6 months after buying the green) use a 2700 psi 2.7gpm honda powered unit that has been in my parents garage for a few years and it is GREAT. Maybe on the verge of a little too strong, but if you're careful it's great. Also works awesome with my MTM foam cannon (far better than the cleanforce and green did)
Id say 2200-2500 psi, 2.3-2.7gpm is ideal for washing cars.
is this it?
PowerStroke
The GPM is a little lower than I'd consider ideal, but it should serve your needs as far as cleaning power.
To put it all into perspective. With the Cleanforce 1800 PSI, I can put my hand about 5-6 inches from the tip with the "general" tip, and it doesn't hurt, or leave a lasting mark. I have accidentally hit my foot with the 2700 before from about the same distance (in highschool washing a deck bare foot) and it left a pretty nice cut.
Think of these tools as "lifetime" tools and get something you can "grow into". Don't limit yourself by going small, it will only cost you more money when you're not satisfied.