Normally, an ADC like F5 sits closer to the servers than clients i.e., client <> F5 latency/distance is greater than F5 <> Server latency/distance. If this is the case in your set up (99% of time, this should be the case), then you can use WAN optimized on client side and LAN optimized on serverside.
I would recommend that you have some kind of valid metric that measures performance before and after the change. I would also recommend using OneConnect with a /32 netmask, if you are not already using it since you are just making (HTTP/S) API calls.