The mrr file format allows for fast display of large raster files, in fact it has a very efficient display of data at all zoom levels. We've found that it really doesn't matter what the file size is (and we've tried some pretty large ones), the opening and display performance is almost instantaneous. They respond well in both MapInfo Professional and Spectrum Spatial Analyst. Have a read of this blog to see a comparison between MI Pro 32-bit Engage 3D and MI Pro 64-bit raster extension:
http://www.critchlow.co.nz/blog/raster-gis-the-trade-off-is-over-with-mapinfo-pro-raster-and-mrr