The 540c is a standard unit and I believe that the Elite is HD.
Sooo...here is my take. For racing you actually want a lower tech, simplier to use, unit. The less detail the better as you are simply following a course and/or looking for hazards. Topography, towns, etc are just noise and confusing when you are trying to haul A$$. So the standard 480c, 540c and larger units really work well in this application. Easy to program, easy to zoom in and out and update really fast.
For play riding in the dez/dunes, I think the HD units from PCI would be great. Tons of features, lots of bling, super detailed, etc. As someone said before you can hook up to tunes, and some even have inputs for vehicle data and create a sort of dash board screen. Pretty trick! If you go this route be careful and ask lots of questions about the antenna. I believe they come with an internal antenna, but they are pretty worthless and update slowly. You will want to get the external antenna, but plan on spending some decent jing on this (I am guessing another couple hundred bucks). PCI also offers some classes on how to get the most out of your GPS.
But for my play riding I just use my color, battery powered Garmin 60CSX hand held that I typically use on my KTM. I just strap that baby onto my XP900 and it has topo, you can upload geo-caches, has all roads, towns etc on it. WAAAAAAY too small for racing but great for play riding.
My dos pesos!
