There isn't a definite order but some suggestions I've encountered and my experience with mine are as follows.
First of all, the original 300/350 mhz machines have a larger power supply than the earlier 9600s. This may not affect you but the early models had 390W (560W for 300, 350 MHz versions).
Usually the controller/bridge type cards (combo USB/FW, ethernet, ATA, etc.) are best in the first slot or high in the box (A1, B1, C1). Video cards are usually the next in line.
The original Twin Turbo that came with mine was a 12" card and was in the bottom slot mainly to be out of the way. I also had an XclaimVR in the E2 slot (next to bottom).I discovered that the TwinTurbo had a definite conflict with my new Sonnet G4 processor so I had to remove it. My slot order now is:
A1 USB/FW combo card (internally connected to power supply and externally to USB hub)
B1 Xlr8 MacFire FW card
C1 Original Mac Radeon 32MB video
F2 XclaimVr 8MB video
I did have to play around with the Xlr8 card to find a slot that worked. I think my D2 slot has a problem as I have not had a card work in that slot as yet. The E2 slot has had a video card in it so it works.
Here are slot orders from some others with whom I have corresponded:
Acard ATA/100
MacSense 10/100 ethernet
Ratoc Firewire/USB 2.0
ATTO UL2D
ATI Radeon Mac Edition 32MB
3dfx Voodoo 5 5500
And another who mixed up the recommended order, yet it works for him.
Video card,
video card,
USB/Firewire card (2 ports each),
wireless networking card,
SCSI controller card,
serial port expansion card (four ports).
In short (I guess it's too late to say that), you may have to experiment to find full compatibility. As you can see it is possible to have all six slots running especially if you have one of the later Mach 5 motherboards and power supplies.
