Legal limit with JSBs is 800 fps so late 800s/900s is only on if you have a firearms certificate.

Having weighed a couple of tins of exacts, although they are nominally 8.44 grain in actuality I had from 8.29 to 8.52.

I wouldn't want the gun to be averaging much more than 790 as you could easily be sent over legal limit with that variation in pellet weight.