The stock settings for level 2 have the settings at 50% on the app, that didn't give me the performance that I wanted so I compromised by setting each of the three parameters at approximately 75% -- this gives me pretty good performance sort of half way between stock level 2 setting and level 3. I do notice that if I do the exact same ride/course with my level 2 settings versus level 3 I get better battery performance and range with my level 2 settings at that 75% mark. I'd say about 20% to 25% better range than level 3, but still with good performance.
On the flats I am riding at around 26 to 28 mph in level 3 versus an average on the flats closer to 24 to 25 mph with my boosted level 2, but with much better battery range - as a rough example. When I am pumping hard on the pedals and pop it from level 2 up to level 3 I still notice a big boost going to level 3. You'll just have to experiment with it on a trial and error basis, but starting with level 2 boosted up around 75% seems to be a good compromise between performance and range for me.