I believe both stage 1 for the 35is and stage 2 for the 35i takes the turbo boost target to what is considered the maximum level that the N54 turbos can run "safely". The OEM tune of the 35is obviously run higher boost targets than the 35i all of the time (335hp vs 300hp), and additionally increased targets are available for a short amount of time.
No matter the actual boost targets, with ESS they are available all of the time. I assume the ESS targets arent much higher than the targets for the 35is over-boost, and even if, it will be hard to feel 5-10% extra torque anyhow. But having the over-boost available all of the time makes sense for example in cooler high speed situations, or if you upgrade the intercooler. It seems like a design compromise when the over-boost function is only available for a fixed amount of seconds no matter the cooling available. On top of that there is the added engine responsiveness and, depending on your tastes, drive-ability of the ESS tune. It does not make the N54 or DCT more jerky imo.
But of course it makes a bit more sense spending money on tuning a 35i compared to a 35is, given that the 35is is comparable to a 35i ESS stage 1 with stage 2-level performance available as over-boost.
I guess the actual psi values are a bit less than what is made possible with the adaptive map from JB. At least I hope so, because I didn't lease mine, and one user here ruined his turbos with JB map 5 (although after tens of thousands of km). . The ESS tune also changes other functions such as ignition timing, vanos position, wastegate control, load limiters, fueling etc but also here details have not been made available so far. Against this I am not sure if the JB can be considered a quality tune, but I like some of the extra functions they added.
EDIT it seems ESS stage 2 runs 14-15psi which is similar to JB4 map 5.
http://www.e90post.com/forums/showth...=193156&page=4