Very true, unfortunately the tuning companies are claiming 25+BHP from just a tune on a Cayman R. I am grateful to the OP's efforts and am leaving my car stock based on these results.Hallonz, I thought the whole thread was quite interesting and I thought the OP put together a lot of useful information from a quality MAHA dyno.
By the same token, given theses cars are normally aspirated I wouldn't have great expectations in relation to peak power but would be more interested in improving the torque curve if and where possible.
The reality is you can't or shouldn't expect to much in the way of gains e.g.
High compression - tick, 12.5 to 1
Direct injection - tick, broad and full torque curve with improved fuel efficiency and decreased risk of knock
Hand balanced engine - tick, elevated redline, improved performance in the kill zone (4k to rev limiter)
Variocam plus - tick, improved inlet 'breathing' and performance above 4k
Given direct injection, the timing is probably reasonably advanced. Thus options are relatively limited to make "significant' gains - obviously if you move to race fuel or E85 (or blends) the risk of knock is further reduced and it is possible to advance timing more and gain power that way (e.g. as shown by the BGB tune - I suspect).
The bottom line, at least in my view, is the gains in a NA engine are so small you are likely better off getting better tires or more advanced driver training if you want to really improve performance. Alternatively, you go the turbo route where substantial gains are readily made.