The cheaper gun I used was a conventional gun. Ran at about 45psi and sprayed single stage enamel. Paint laid down great with that gun, but due to being conventional did have to worry about dry spray as the overspray was much more than a HVLP.
I run my HVLP gun at around 20-25psi. It sprays better than my cheaper gun and has much less overspray. Best way to find out how it will spray is to experiment. First time I painted a car I used a siphon feed gun that had a large cup. If you weren't careful when painting a hood, roof, or decklid you could get the bottom of that cup in the paint. Plus you always had paint leftover.
If I were you I'd start priming and experimenting with the guns you have now. You can always find a small piece on your car and paint it with the gun once it is prepped and ready. That will let you know how the gun will work and you won't find out halfway into a paint job. When I paint I try to take as many panels as I can off and paint them seperately. I also try to paint the car in sections, especially if it is a big car. Cuts down on the chance of overspray causing dry spray on fresh painted parts.