Anyone have any experience with using non-Mapsource maps on your Garmin GPS?

I've loaded one quadrant from a translated geo-tiff map (that I use as my base maps for Memory Maps).  I can load the map with no issue.  The rub I've encountered is that map rendering is PAINFULLY slow.

Anyone have a different experience?  Yes,  I know that the amount of detail on a geo-tiff map is significantly larger than what you find on a Mapsource map.  But, if this is what you have to put up with, it makes translating satellite images not worth the effort.

Is there is another format that makes more sense to translate into an IMG file?

dd