That'll depend on the engine/prop combination. Power available vs IAS will drop off more on a fixed pitch as speed reduces and full throttle RPM reduces.
I've not got the data points for mine, but I'd guess about 80 KIAS for Vx and 100-110 KIAS for Vy. Do some timed 1000' to 2000' climbs at different airspeeds and you can calculate what it is for your set-up.
You seldom need to use either unless you're trying to impress
