Correct size for Thermostatic valve and controls

Hello,
Can anyone tell me if a 3/4 thermostatic valve is the correct choice (vs the 1/2 model) when used with both a shower head and a hand held shower unit? Each shower head will be controlled by volume control. Not sure about whether to use 1/2 or 3/4 inch for the volume controls. The hot and cold water feeds are 1/2 inch. My water pressure is 50 PSI with a flow rate of 7 GPM. If I was to use the 3/4 inch parts should the piping be 3/4 inch or reduced to 1/2 between the thermostatic valve and the volume controls and the volume controls to the shower heads?
I contacted the Manufacturer, Grohe, and all they said was that with 2 outlets I could use either. They were not much help.
Thanks
Steve Odian

By federal regs, a showerhead can't use more than 2.5gpm, so with two heads max, it probably won't make much difference...I concur. It gets to be more of a factor if you've got more heads. The 1/2" valve is less expensive. Now, if you had 3/4" supply lines and were filling a big tub, that would be a different story.

jadnashua

Thankyou for the response
Steve