I tried a friend's DSL40C a few weeks before I ordered my HR, and it actually put me off the idea of getting a Marshall for a little while. The DSL40C at low volumes was everything I always thought I disliked about Marshalls: strident highs; loose, grainy, "blatty" gain. Plenty of gain but not necessarily in a good way?

Also, the front panel got hot enough to take your fingerprints off

which was weirdly distracting. Granted, I didn't spend a whole lot of time trying to get it dialed right - maybe I missed something.
The 100HR is night and day. The gain is much more modern sounding to my ear, and the EQ was easier to wrap my head around. Some of this may be down to changes in the circuit (esp. EQ) since the 40C was current; probably more is a result of running a closed back 4x12 vs. a little 1x12.