Darryl this is too funny - I had a Monterra, and now have a Montana 650.
The Monterra suffered a tragic caching accident during warmup caches for GAG21. Apparently the screens aren't meant to survive getting angrily launched into the air and landing on a gravel pathway. The unit had dumped all my cache text data for the last time and I saw red. Between that and excessive buttonology, a compass that never calibrated, high power consumption, and a map zoom that was terrible for caching, it was only time before I dumped it anyways.
For maps I was using the downloadable OSM & Ibycus ones. One had better street info for in-city caching, one had better trails, woodlines, etc for out in the greenbelt and further afield. I haven't tried any Garmin brand map cards.
I bought a 650 about an hour later at LeBaron's on Merivale, and am quite happy with it. Took the microSD card with the maps out of the Monterra, put it into the Montana, and it worked like a charm.
GPC