Hi Chris,
I think the standard kit pistons in the MP9 SE are 1.2 x 8 front and 1.3 x 8 rear.
When I've ran the tapered pistons they were good, but so are the standard straight holed pistons. As Simon said, the 1.3 x 6 hole all round are a good starting point, when I was testing with Rob over at Deedale last weekend I ran the following:-
Front
1.3 x 6 with 450wt Kyosho Oil and Blue springs
Rear
1.3 x 8 with 400Wt Kyosho oil and Green Springs
The car had enough pack to handle the big jumps there, but was also able to soak up the smaller ripples and bumps too.
Hope that doesn't confuse things for you
As I mentioned in a previous post, if we ever meet up at a meeting you're more than welcome to come and try out pistons/springs etc; I've got plenty you can try out.
Colin