PCI E slots of Asus P6T

Hi,
I'm planning on getting the Asus P6T vanilla version for my i7 920 system.
I was wondering how the expansion slots work out.

I can tell that there's total 3 PCI Express 2.0 slots..
and the description says it works as 16x/16x/4x in Tri-SLI configuration.
However, what happens if I put one card at the top slot, and another at the bottom
instead of two adjacent at the top?

so it's like

=======================
GFX CARD |
=======================

====================== <- PCI Express slot

===================

=======================
GFX CARD |
=======================

Will it run at 16x/4x, or 16x/16x?
I want to do this so that there's space between my two GTX 275's, so there's adequate airflow.
I'm using a mid tower (storm scout) and I dont want the two cards to be stuck together to worsen the flow,
since two high end cards in a mid tower is already a heat-seeking problem.
thanks