The screen sizes might be different. The XSGA+ at 1400 x 1050 is very nice, or the UGA at 1600 x1200 is nicer. The 8100 can hold two batteries and still have the CD drive. The 4100 can only hold one plus the CD. The 8 is several pounds heavier than the 4 and if you are going to carry it around every day, I would want the 4. Other than the size and the bays, they are pretty comparable in performance.