Guido stepping down from BDFL may indeed be what allowed the recent speed improvements to progress; but certainly not in the way you're implying. If there is a causal effect here it seems more likely that it's because it has allowed him to concentrate more on the speed improvement work than he otherwise would have with BDFL issues taking up his time.

From what I've seen Guido has been quite actively involved in the speed up work, somewhat in the actual development but even more so in getting it merged (a problem many previous speed up attempts have failed at).