You're making it too easy for yourself. You want the dev to go through all the changes from the last few weeks and guess why one of them is slower for you and not for him? This won't work, please see which is the first version you're having trouble with. It should be easy, going through the patches.
it's not that hard to go through them (I can just browse through my hg commit history)
but thing is I want to investigate any potential performance problem regardless (even false alarms)
(e.g. all through testing I thought the particles were optimised because their rendering was optimised
and turns out they were a cause of a major performance drop because I forgot that some of them also check for collisions)