I am glad I found this board and starting reading. I also was in the 335 crowd but had been off the boards for awhile. I did some data log recently and your ignition timing appears to be significantly retarded. I am catless but otherwise stock and have a tune from one of the big tuners. (won't say which only because I don't want to post data without them knowing that gives away what they do).
Anyway, I did 2nd and 3rd gear WOT pulls with IAT in the 68 F range and just looking at the 6500-8500 range which is all I cared about my timing was pretty much 34 degrees throughout that range with AFR of 29 (these numbers were give or take .0x of a number).
Your timing, unless I am missing something appears to be as much as 10 degrees or more retarded than mine. I use 94 octane fuel.
Logging knock values I showed no knock until I reached 8500-8600 where timing dropped to 31 degrees and some knock showed up on the logs. I am guessing the higher load at that high of an RPM is too much to handle.
I was going off the basis that I believe the stock timing targets for a WOT run given ideal conditions was max of 32 degrees. I was a bit surprised I was only 2 degrees higher than this with a tune and pretty ideal conditions with no knock tells me timing was not being pulled.
Of note I did have a LTFT value of 4 that was logged. Not sure that matters here.
It is very hard to find information on datalogs for the m3 or any sort of stock targets for AFR, ignition timing etc. I would love to see a stock timing map or atleast see the max stock timing targets to compare.
But something appears to be yanking timing and I am guessing you may be on 91 octane? IAT's look the same as mine which was in the cool range and unless you were going uphill or something I don't see why timing would be pulled over 10 degrees almost steadily throughout the last 2k rpms which is essentially the entire powerband in 3rd gear.
I would love you to do more data-logs and I am going to continue the same with 2nd and 3rd gear runs.
I would include a value to pick up whether or not you are knocking and maybe the AFR to see a bit more data to determine whats going on with timing. 10 degrees through the powerband under cool IAT's with no other problems would be a significant loss of power and something you want to reclaim unless I am absolutely wrong about the stock max timing target of 32 which in that case maybe the stock max target is in the 24-25 range?