I haven't tried throttlestop past 7 beta 3, didn't realize it had been updated for broadwell. I'll have to go check it out. In order to control thermals and tweak performance I've been using Intel XTU 6. XTU 6 added support for broadwell. If you aren't familiar it allows for under/over volting the cpu and gpu, changing multipliers, long and short turbo windows, wattage, etc. Basically anything that the intel chipset allows that the manufacturer didn't lock down. I use it every day with my m18xr1 to run my 2920xm at 4.9ghz x4 with HT. Wonderful software, just got to make sure you grab the correct version for your chipset. 6.0.2.2 works great for the 2015 12" Macbook and best of all the wattage and voltage settings persist from windows to OS X. Actually allows me to 25m raid in WoW at reasonable frame rates at 1280x720(everything on low but particle effects on medium, projected textures on, texture resolution high, view distance high). BTW, huge overclocking nerd...I generally only lurk for years. Made an account just to respond to you. Link to latest XTU below.
https://downloadcenter.intel.com/download/24075/Intel-Extreme-Tuning-Utility-Intel-XTU-