Having sized a lot of water treatment equipment over the years for the peak demand you have been talking about, and then selling that equipment all over the country for the last 7 yrs to customers that I am sure would tell me of problems or post them in my customer comments forum if there were any, you are going at this all wrong.
First, you aren't installing just a control valve. You are installing a whole softener.
Y'all go on about what size valve because Bob999 doesn't know how to size a softener and yet sounds as if he does and says I'm wrong about the 1" Clack valve because he read something here or there... problem is he doesn't understand what he read or how to use it and I'm not going to educate him anymore.
You need a softener with a constant SFR gpm higher than your peak demand gpm. The constant SFR is dictated/controlled only by the volume of resin in the softener (and not using the figures Bob gets off a resin spec sheet).
The volume of resin dictates the size of the resin tank that must be used and, the size of the tank dictates the control valve that can or can not be used. That means that you do not need the ID of the porting of the control valve to match the ID of the plumbing (although a code will call for no reduction of the plumbing connectors). All that also means the distributor tube ID doesn't have to match the porting of the control valve or the ID of the plumbing.
You are seriously oversizing the ID of the plumbing; from what I recall of all that has been said here, 1" would be sufficient now.
[FONT=Arial, Helvetica, sans-serif]The flow rate from an open ended 100' of 3/4" pipe at 50 psi is 17.5 gpm, for 1", it is 37 gpm. At 30 psi, 3/4" is 14 gpm and 1" is 28 gpm. Of course you will not get that much flow if you have the same ID pipe because your plumbing includes tees and elbows and valves which cause pressure losses and the fixture risers are much smaller ID than the pipe feeding them.
Are you going to have a 1.25" or 1.5" shower valve or shower head/body sprays? I think not, most likely, at best you'll have a 3/4" and 1/2".
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You will not notice a pressure loss with a correctly sized softener and for up to a 21" tank (7.5 cuft) a Clack WS-1 will work just fine.