I haven't been caching for long either, but I have used both the eTrex Legend and Rino 110 at the same time. I really can't say about the higher end units that you are looking for, but between the two of them, heres some finner points that I noticed. It might help you know what features you should check on.
+ I love the screen on the Legend. Although I think it is physically the area as the Rino it has ~50% higher resolution. I would go for the higher res screen.
- Patch antenna Good Reception in the Car. Not so good reception in the woods.
+ Helix Antenna Good Reception in the Woods. Not so good in the Car.
+ 2 batteries. I like to use rechargables, and the Rino uses an odd three batteries. (they don't make a 3 battery charger, and mixing batteries at different charge levels, is not recommended)
+ If I am using the Routing function while driving I like the speaker on the Rino to tell me that a turn is coming up. Although just a simple beep (compaired to some speech models), I find I don't have to keep looking away from the road as much.
- I though 8 MB was a lot when I had the Garmin Canada mapSource 3.02, and I could put all of BC in there. I recently bought Canada version 4.0. These maps are HUGE, and can only hold ~100 mile radius of a major metropolitan area.
I kept the Rino because I thought the Radio is neat, and I Since I know other people with the rino, we can sent our location to each other. Otherwise I would have kept the Legend. It's a great little unit. I will soon upgrade to the rino 120 or 130.
Kenji