Rolling roads in Southampton area?

[M5MarkM]

Anyone recommend a rolling road facility in Southampton area? Don't mind if it is a little further afield. I want somewhere that measure 600bhp+ as I'm curious what difference my exhaust mods have made to the Vanquish S

[M5MarkM]

Tried all of them, none open on a Saturday and most booked up for a few weeks, so much for that!