I need to outfit some of my field staff with iPhones. They will primarily be used as hot spots. On Verizon, is there any appreciable gain in OTA network speed between the 4 and 4S? I know the AT&T version is faster, however I need to stay on Verizon.
Since you appear to only want the gains to be for tethering, then I would say no, the 4S would not be worth the money for you.
The higher capacity of the 4S antennae's HSDPA is not supported on CDMA, you would need a supporting GSM carrier to take advantage of this. So no, you will not see a difference in network speed itself.
HOWEVER! Much of the sense of speed is in the phone hardware itself. Your phone needs to render the data it receives in browsers and apps. So you would still likely see performance gains that may appear to be network related, but are not, from upgrading to 4S.
Caveat: Might as well wait for the new iPhone model this year if you're going to be throwing down any money for handset upgrades.