I have been using the 7D with the ST-E3 and 600 EX-RT's for over a year now.
Never had a problem with sync speed of 1/250 on any of my images. Never had a problem using HSS too.
You will see the the TV icon warning show up on your master ST-E3 when shutter is 160, 200 and 250th. However, all images are fine regarding banding issue associated with shutter speed above camera sync speed.
Still have not heard from Canon as to why this misinformation is still in print.
Besides myself, several other Canon CPS members I know and Syl Arena who travelers the country with wonderful Speedliting Intensives, have all supported our conclusions above.
Unfortunately, GROUP will not work on the 2011 cameras and prior. This a feature that I miss on my 7D. Guess I have to get on the Good List for Christmas this year.
Canon 5D Mark III (x2), BG-E11 Grips, 7D (x2) BG-E7 Grips, Canon Lenses 10-22, 17-40 f/4 L, 17-55 f/2.8 IS, 24-105 f/4 L IS, 70-200 f/2.8 L IS II, 70-200 f/4 L IS, 100-400 f/4.5-5.6 L IS, TS-E 24 f/3.5 L II, 50 f/1.4, 85 f/1.8, 100 f/2.8 L Macro IS, Canon 1.4 Extender III, 4 Canon 600 EX-RT, 2 Canon ST-E3 Transmitters, Canon Pixma PRO-10 Printer