Wouldn't break the board, but allow for undoubtably unsafe installation of a mainstream pcie 2.0 capable graphics adapter in a pcie 2.0 x4 lane slot? According to the article about pcie 2.0, that'd equal the x8 lane slot (physically looking like a x16 lane one) on my p35 - so it would be possible to run crossfire on a micro atx board with only 1 16x slot and a 4x slot ? (unless other stuff on the board is physically limiting the length of addin cards...)

Microatx boards do not support crossfire, or pcie2.0, for that matter. It won't work. No offense, but the idea is just stupid.

In most cases it would be stupid yes, but not in the case I'm considering. I've made it a habit of having custom computer cases, and one of em is a tube - which happends to be rather big, as a standard atx board has to fit into it. If I were to use a micro atx, I could perhaps even make a small ball to install it into ....

You need 1 of these : http://www.ably.com.tw/pdt/viewpdt [...] PCIE_RISER

And you'd still be running CrossFire 16x/4x so don't forget an extra long CrossFire bridge cable.

oh my! that's even better! no breaking the warranty of a new board ... and much easier to fit into a custom chassis
thanks mate

No problem. There's a riser for just about everything these days.