Definitely the second one with the horizontal horizon.
The reason?
It is
authentic. I think authenticity is important. There's far too much fakery these days, and people fall for it, largely because the genuine is so hard to find. I realise this wasn't intentional fakery, but nevertheless the effect of the first version is to fool you into thinking that it's more dramatic than it is. Some people may like that, but I don't.
In this case, you look at the horizon on the straightened version, and you look at the boat, and you know how much it's heeling over.
In the first one, the immediate impact is greater, because the lean is exaggerated, but it's not real. Then you look further into the picture, see the horizon, the effect is lost, for me at least, because I realise I've been had.
So I think the straight version is far superior. Losing the top edge of the spray is a pity, but minor in comparison.
In any case, leaning over more does not necessarily mean going faster.
PS I think you were very brave taking the K10D out and using it for that shot. Thank goodness for the seals, eh?