Your Garmin help, please

I think I'm going to buy a Garmin next week - sick of faffing around with gps tracking on my blackberry and my Polar computer is fiddly and irritating. I've pretty much ruled out the 500 as I don't really see the point forking out if it doesn't have maps... so questions are:

a) 705 or 800? Is the 800 significantly better?

b) maps etc? Should I bother paying for these or are there backdoor alternatives? I'm a Mac user if that makes any difference..

Thanks in advance.

http://www.bikeradar.com/forums/viewtopic.php?f=40012&t=12849481