I'm a music producer and just ordered the 2,9 MBP for live and movie studio use, so CPU power is the main concern for me. I did some homework on the 6920HQ and found out that :
-haswell cpu's had higher turboboost, which is shown in synthetic benchmarks as Geekbench, but under sustained load on multiple CPU cores (which is needed for audio workstations) performed at actual 2,8-3,0 Ghz frequency, ref. read this really good review about the 2015 macbook pro in performance and processor sections:
http://www.notebookcheck.net/Apple-MacBook-Pro-Retina-15-Mid-2015-Review.144402.0.html
-confirmed in the same article, because of this, 4980hq where roughly on a par with other 2014 or 2015 options under sustained load (out of experience, in concrete DAW use there is not much difference between different MBP)
-skylake cpu's have the important advantage for notebooks of the lower tdp, resulting in less (no?) throttling when under sustained load. On top of that skylake is presumed to deliver 5 to 10% speed bump per (actual) Ghz vs Haswell perf./Ghz ratio.
--> You can actually see this in the Cinebench R15 CPU scores which should measure real (as opposed to theoretical), sustained performance. 2014 and 2015 MBP's scored around 600 on this multicore cpu test (see article above). While the 2016 mid-tier MBP (6820HQ) as reviewed by Ars Technica scored a promising 700 on the same test (this is the only cinebench CPU test I could find for the new 15 inch MBP). See
http://arstechnica.com/video/2016/11/the-2016-13-and-15-inch-touch-bar-macbook-pros-reviewed/
--> I didn't find 6920HQ macbook pro cinebench CPU scores yet (anyone please? or Prime 95 etc.?), but if there are no throttling issues we could be expecting around 750 on the same multicore test (see other 6920HQ laptops). If this is true we could thus be expecting 10 up to 25% faster raw multicore cpu power when on high load when compared to the previous MBP, which would be the first significant speed bump in years for the 15-inches... We payed enough for it, so we may always hope so
-Perhaps a detail, but i read somewhere that speed stepping is handled differently in skylake cpu (not by OS but within system), resulting in lower latencies when sudden bursts of cpu power are needed. This wouldn't be accurately measured yet in geekbench. (sorry but I lost the source, it was on macrumors however)