Had a few of these now and the main hardware differences are:
Fluorescent to LED Screen
Sluggish to Faster processors
Sluggish to Faster software
HDD to SSD
Versions A to C are incredibly slow to boot up and operate compared to say, an H or Q. These are all HDD.
Version Q compared to R, S or T (SSD) has a barely perceptible difference in performance.
Battery drain can be controlled by internal software on the newer ones, rather than replacing the Can Gateway.
Newer ones have full 7 digit postcodes in the nav software too.