I asked Outlaw the same question, and here is the reply that I received:

"When comparing the Model 770 and the Model 7100 at modest listening levels with moderate source material the units would sound almost identical, sonically. However, if you were to move to a scenario where you were listening at higher volume levels or listening to material that includes more dynamic passages the difference between the two units would stand out more profoundly. The increased power when moving from 100/165 (4 or 8ohms) watts per channel to 200/300 (4 or 8ohms) watts per channel is much
more evident when you're forced to draw on the amplifier's storage or simply require more power. The increased power will provide a great deal more accuracy and detail in dynamic passages and louder listening levels."

The main speakers that I own and plan to use with the outlaw 950/amp combo are somewhat large and only moderately efficient (Mirage M3si, 86db), so I'm choosing the 755 over the 7100 just to be safe.