From my limited knowledge shouldn't one aim for around 11:1 for max power, on gasoline of course ? but lambda is lambda so 11:1 should be relevant to e85.
Nope, max power on gasoline should be at 12.5:1.
Yes lambda 1 is lambda 1 and stoich is stoich but that doesn't mean that 11:1 gas A/F is 11:1 E85 A/F.
If fact if your running E85 and your gasoline calibrated A/F gauge says 11:1 your actually be running roughly a 7.3:1 E85 ratio which is way richer than you need for safely making power on E85 due to it's high octane and charge cooling properties.
Generally people tune E85 to a 12-12.5:1 gas A/F which equals about 8-8.3:1 E85 A/F.
None of which really matters, just tune using your gas calibrated A/F gauge like you usually would, it just takes ~30% more E85 to do it.
should be tuning to 11:1 gas A/F if what they are after is max power.