Yeah - I actually have a Dell XPS 15 coming tomorrow (from Dell Outlet - so a 9560 7700HQ/16GB/512GB/4K for $1,149 and 16% cashback through ebates).  Then going to decide which one to keep.  I still want to keep the Mac, but I just don't know if I can justify over 2x the price for not much performance gain - basically just for OSX... 
But yeah I know all about undervolting.  I plan on doing that to the Dell XPS to see what type of results I get - maybe even repasting the Dell too.  Then seeing which performs better for my use cases and deciding what to do.  But now that you mention it, I might as well give it a go on the MBP too.  If I remember and do this after work, I'll post what results I get.