Have you considered the MobileMapperCX? On my favorite want list.
I'm making do with the older model MobileMapper, and a 60CSx.
When I set up the 60CSx to display in Grid ft, then test with WAAS on/off, over 10 min to enable, and watch for 10 min after disableing it, I get no change in the location, or +- location. This matches what Garmin emailed some of us in 06, about the engineers had found only about a half of a foot improvement with WAAS over the SiRF chip. Said that they probably would drop WAAS on the new x units at a later date. They sure stirred up a ruckus over that!
Both of my units do good under trees, with thee 60 being a little more jumpy. I have gotten well inside of 2 meters, when at a surveyed point, out in the open, with ideal Sat lineup. Trees and bad PDOP, can be another matter.
I'm tempted by some of the prices on ebay, at the moment, for the MMCX.
Magellan Pro is now Ashtec. DL the manual, and related, to give you some ideas about the CX.