I am about your size (78kg, 182cm) and have a 2010 isonic 121(75 wide). It handles a 9.0 nicely and starts planing with 9.0 around 12-15 knots. It probably wouldn't handle a 9.5 and especially 10 as much as it seems like you might want, but it definitely has lots of top end. Still quite comfortable with 6.7 and 36cm fin. So, if you want more top end and only a bit bigger than your manta 69, a 75cm isonic121 (or 2011 117) would be a good way to go. If you want just a bit more low end, the 80cm 117 wide should do it.
I have sailed other 85cm wide boards and find them limited on the top end...might as well go with a formula at that point unless you really need to optimize reaching speed in under 12knots of wind.
Hope this helps,