340 is a bigger bore to start with. The most important choice for me would be the pour number. The lower the number the less porosity . 340-1 being the best and 340-8 and up being the worst. The lower numbers seem to always sonic test thicker and more consistent bores. One thing to remember is once you stroke it there is more side load on the bore.
I had one let go at 7500. The only thing that remained from the cylinder was the studs hanging out of the head. The piston poked its way through the bore and all I heard was the sound of marbles in a can. Oiling the tires at the end of second on the street is not an experience I'd would want to relive.
