Fileserver has ~85MBps PCI limit (Intel-recognized i850 errata). Should I go with Firewire over AGP or Gigabit over PCI?

[CZroe]

All i850-based boards have a maximum PCI bandwidth of 85MBps instead of the normal 133MBps. PCI bus overhead and shared bandwidth with other PCI devices makes PCI Gigabit adapter performance suffer even with the normal 133MBps limitation. The thing is, I'm running a Promise SuperTrak SX6000 RAID5 card with six 120GB WD1200JB drives on that bus and expect to make multi-gigabyte transfers over the network frequently (DVD & CD images, XP Media Center Edition recorded content and such for archival AND consolidated access). That if Gigabit networking alone will max out the 85MBps bus, then there will be TWO PCI bus-saturating devices on that bus if I add one and I will get abysmal performance from both devices.

The ATI All-In-Wonder 8500DV has a Firewire port with a PCI to AGP bridge chip. That would at least avoid saturating the PCI bus further, but will it really be faster? Typical low RAID5 performance probably means that I wouldn't loose much performance from the array should I add a Gigabit PCI card, but because I do not have the money to expirement and because I have never used either Gigabit or Firewire networking (Save for a quickie laptop connection to my desktop once with a super-cheap cable), I would be able to estimate what kind of performance I would get from Gagibit PCI. Would it be less or more than Firewire's rated 400mbps?

Are there any other solutions? A strange PCI card connector for AGP perhaps or an unheard of AGP Gigabit card?