I'll admit the second card sure makes for a tight squeeze, wires are all over I have them behind and inside cages I hide them as much as I can but a cable management system was not apart of the NSK6850 features when I bought it.
I am running a raid setup with my 2 drives and I am thinking thats what the problems is, I enabled sata ports 3-4 in the bios but everytime it gets past the XP Loading screen it bluescreens and reboots. I am assuming it does work due to the fact that I get past the xp loading screen and then the driver configuration causes a fatal exception. I am going uninstall my drivers and hopefully that will prevent the fatal exception from happening because clearly there is a conflict somewhere.
I will let you know how it goes.
Update: Well to no avail I tried ports 3-4 and 5-6 and it blue screens everytime I even tried booting into safe mode and I get the same result and to top it off my card is already on its way here, I should have it sometime this afternoon and I won't be able to use it at all in SLI. I did get an interesting error from Windows stating that my anti-virus software caused some problem I wonder if there is any indication that norton might be interfering with the startup sequence as windows begins to load. To be honest I believe that this on a much lower level then that simply put I would have to re-install windows on ports 3-4 to start with, but even so I have no idea if that would solve the problem outright and I am not about to do that as I have far to much stuff downloaded and installed to consider it. 
No sli for me,
EE