Marginally... the gigabyte boards using them get 4% lower power consumption compared to the reference boards
I'm not an expert on the spec, but I'm fairly well versed on it and nowhere, unless theres been an addendum I've missed, does it specifiy any overall hard limits, theres regulation on the limits of what can be drawn from each individual PCI-e standard power connector and various advisories but the rest is left to a guide for thermal and electrical management in desktop systems and aslong as the developer can show they've taken that guide into consideration there should be no problem getting ratification.
There may not be an actual hard limit, but as said above, major builders won't go for anything more than slot + 6-pin + 8-pin power consumption. It just wouldn't be worth their time and effort and has been that way for quite a while. Still seeing Dell et al with 400 watt psu's and no option to increase it