Shaggy Sheep Driver. In a max rate possible turn you are on the buffet at max allowable g but that won't be very fast. You can work out the speed by taking the square root of your max load factor and multiplying it by the basic stall speed. This is actially the manoeuvre speed for an aircraft - the speed at which you can pull to the buffet without overstressing the aircraft.
However, if you have not received any instruction in this technique DO NOT TRY IT for the following reasons: it will generate a horrendous rate of descent; a moment's inattention and you will come off the buffet, and the speed WILL race towards VNE as well as busting max engine rpm if you don't have a VP prop; finally, and most importantly, if you're not used to a sustained high 'g' you'll probably black out and may or may not come round before hitting the ground - I blacked myself out in a Jet Provost when solo a long time ago and do not recommend it.