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I'm late to the party, but I figured I would add to this DCT vs Manual discussion since I researched this issue thoroughly myself first on E92 M3 and then on this car.
DCT is a definite advantage on track because a manual clutch has a small interruption in power delivery every time you shift. Each shift loses a tenth or two which add up to a couple full seconds or so over the course of the entire track. However, manual cars gain some of that time back in the corners due to the ~40-60lbs (depending on the specific car) weight advantage of the manual. On any large track, the weight advantage does not do enough to offset the power interruption, and a DCT will be ~1 second/lap faster.
As the size the track decreases, the DCT advantage decreases, as more time is spent in turns versus the number of shifts on straightaways. However, one wrench in this is that DCT's allow shifting during turns, which means that DCT's can always be in the optimal part of the power band while manual shifters will often stay in a suboptimal gear in order to avoid a gear shift at an awkward time.
When you get down to an autocross size course, straights are effectively gone, removing the primary advantage of DCT's. However, the secondary advantage of shifting at awkward times remains. Most autocross courses can be comfortably driven in 2nd gear the entire time. However, some courses have slow corners that benefit from briefly shifting to 1st or straights just long enough to bounce off the limiter in 2nd. Most drivers don't bother shifting in those instances because the shift itself will negate any advantage in changing gears, but DCT drivers can shift without penalty.
Because autocross courses vary so wildly, it is impossible for anyone to say with certainty whether DCT or manual will be a definite advantage. One may be advantageous one day, while the other on the next. Because autocross courses are short, it is unlikely for the difference between DCT and manual to vary more than a tenth or two, and most are pretty close to a wash.
One final note. DCT cars tend to me more difficult to launch reliably, which only matters for SCCA ProSolo's. The issue is launch control is only available on the first run (most cars require more cooldown to use launch control again than what a ProSolo typically allows). Launching DCT's manually is a bit awkward because the computers dont like to quickly switch from N to D. If doing well at a ProSolo matters to you, that may increase the value of a manual.
ProSolo's aside, I believe DCT vs manual is driver preference for autocross. I myself got a DCT since a good example was locally available (saving me thousands of dollars in transportation) and it is a daily driver that my wife will borrow from time to time.
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