Answer
This problem is addressed in ArcGIS 8.1 Service Pack 1. See the Related Information section to download this pack.
Raster layer drawing performance within ArcGIS is unacceptable in many cases; however, many of these problems are now addressed, specifically RGB and Grayscale raster display in ArcGIS 8.1 Service Pack 1. More work is continuing with regards to Pseudocolored and 1-bit Raster display performance (to be released in a future release/service pack).