If you are not happy with the display speed of maps while driving you can try some of these tricks for improving Garmin map rendering performance which make a noticeable difference on most units especially the older models.
Firstly the most common cause for jerking map panning on a Garmin GPS unit is slow loading from the SD card, now this does not mean you have to go out and buy a new SD card, you can rather change where the maps are stored to improve performance. You will need to use Mapsource or the Map installer provided by Garmin to achieve this. The older units do not have much built in storage so it is unlikely that you will be able to load the entire mapset on the device.
The solution is to add dense or high detail areas to the device only, load the cities onto the device only and the rest of your maps onto the SD card, when selecting which maps to load you will notice that each grid is labelled so you just need to keep track of which grid blocks you load onto the device and skip them when loading the rest of the maps onto your SD card. You can use a similar tactic by loading your street maps on the unit and your topography maps on the sd card and disabling the topography maps when not in use.
Other things to try:
Reduce the rendering detail level in your map settings found under:
Zoom in to reduce the amount of data required for the unit, you will notice that Garmin devices actually automatically zoom in while navigating for this exact reason but if you are not currently the navigating the zoom level could be far enough out to overload the screen with data which the unit needs to load up from the cards. Zooming in means there is less data being loaded and can make a big difference.