For NG at least there's a 65 knot spread in the minimum speeds one can
normally expect to fly between clean and F40. The first 40 knots (c60%) of this reduction in minimum manoeuvring speed (not stall speed but I don't have that info) is attained by the time F5 is extended, so just like most aircraft, any flap beyond roughly half scale deflection tends to do little if anything for stall speed reduction and a lot for dragging you up. Which one may argue would lead to a steep flight path when there's no thrust available to flatten it out and that means there's less margin for error in a situation presenting a different visual aspect to what one has ever seen before (anyone done it twice yet actually?).
As for the ditching button on the bus it appears to seal everything up below the waterline. Scratching away at very feint memories here but on the NG doesn't the overboard exhaust valve open when there's low cabin diff and/or the flaps are not up? Hence it can't be completely sealed? Same story for the ram air doors? Personally I don't think I'd be hanging about long enough for these items to be of practical significance
