Have half-stop, will bid 3NT

The above piece of chutzpah at Matchpoints won me 87%. I reasoned thus, holding 6 card diamond support and the HA and the S QJ, maybe they could run spades on me but it was matchpoints, not money. The better bid was perhaps a scientific three spades, lest partner should have Axx in spades. As it was, the spade lead set up my ninth trick. (No lead threatens me. If H is led i hold up till round 3.) When it was ducked, I went safely to set up a club. Now a heart return is needed to hold me to nine. But that is a bit double dummy. Even nine tricks in game would have been 72%. The field was all over the place 3D +1, 4D = etc.