Andy,
You have a point about useful load. Obviously they vary according to equipment fit and age, but according to the Piper web site,
http://www.newpiper.com , the standard useful load of a Warrior is 907 lbs/411 kg, and of an Arrow 960 lbs/435 kg. Not much difference at all. You can sure feel the difference in the all-up weight, though!
Another significant difference, which I forgot to mention before, is that the Arrow has much bigger tanks than the Warrior / Archer. So if you fill 'em up, you're in two-seater territory. However, you don't need to fill them all the way, and if you're flying any distance I suspect a properly leaned 200 hp Arrow with the revs back, gear up and a fairly modest MP setting is probably using less fuel per mile than a 160 hp Warrior trundling along at a higher throttle setting with fixed prop and gear.
Personally I like the 180 hp Archer II best of all the PA-28 family. Usually lighter than an Archer III, and doesn't have those flush-fitting fuel caps that seem to let the water in. But I wouldn't mind a go in a 235 hp Dakota some time, it sounds like fun.