It is suggested that you maximize your PCI performance by choosing a motherboard with a chipset with the best PCI performance. Delays, Reverbs, and Samplers all use PCI bandwidth, and although in theory most current boards should have 133mb/sec, in reality some boards have less than half of that! This of course leads to the "PCI Overflow" problem, but can be avoided by choosing a motherboard with a tested chipset.
It's suggested that you get the most simple board with the least onboard devices, as usually even onboard devices take IRQ resources, etc - sometimes they can be disabled, sometimes not - so unless you know for sure, get a no frills board with a solid chipset.
Motherboards:
Pentium IV + DDR -- Any board with Intel i845-DDR, I have three favorites, ASUS P4B266, Intel D845GB, and Abit BD7.
Pentium IV + RDRAM -- Any board with Intel i850 chipset performs well, I'm using ASUS P4TE with great success. Better memory bandwidth but slightly less PCI than i845-DDR. Also the Intel D850MV or D850MVL if you need network. We also use the D850MVL with great success.
Pentium III + SDRAM -- Any board with the Intel i815E, i815EP, i815EP vB. My current favorite hands down: ASUS TUSL2-C. Even more reliable, but not quite as high performance: Intel Motherboard D815EPEA2.
General P4 information: At this time if buying a P4, you will definitely want to make sure you get a Northwood core. These have 512K cache, double the previous P4 cores, and run cooler. A 2.0A seems the best price/performance ratio until the 2.2A Ghz version drops a bit more.
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So far, for AMD, the tested chipsets include KT133A, KT266A, AMD761. Soon to be tested nForce (although nForce 415 looks a lot more interesting for our purposes). Future testing: SiS745 (once the ASUS board comes out). SiS735 will not be tested, although some have said they get great results with it - reason - no top quality board makers have a 735 board out, but will have a 745 out in the future.
The best chipset for PCI performance is by far the AMD761. Three favorites, ASUS A7M266, GigaByte GA-7DX, Epox 8K7A. Do expect much, much <b>less PCI performance</b> compared to the Intel solutions, but if you're using lots of VST/native plugins and rely on outboard reverb units, then this might be the perfect solution for you. The AMD CPu's price vs. performance is hard to ignore!
SCSI is not suggested, as IDE is cheaper, runs quieter, and, at least on the Intel chipsets, the onboard IDE header does not eat any PCI resources (generally, onboard RAID headers DO take PCI/CPU resources, something to keep in mind). Large SCSI RAID arrays on a traditional desktop PC literally take most of the available PCI bandwidth - if you want SCSI and want to use PCI intensive DSP devices like realtime samplers, reverbs, delays, then it is suggested you get a Workstation/Server motherboard with dual PCI buses, one bus for your DSP boards, etc, and one bus strickly for your SCSI array.
The only chipsets which should be avoided if you need to use anything related to the PCI bus, are VIA chipsets. The problems with PCI bandwidth issues with VIA chipsets are well documented around the web, and other people with PCI intensive devices have found a problem with ALL Via chipsets as well - including the KT266A. There is some 3rd party patch that may help this, but until this is fixed by Via themselves (ie: in a VIA 4-in-1 update), or unless you understand how to fix this issue, it's going to be suggested you avoid these chipsets.
(Note, the AMD761 Northbridge is often times paired witha Via southbridge - this doesn't seem to effect the PCI performance so much.)
Dual processors can also be used with Creamware, but you really should run duals only under Windows XP Pro, otherwise you might run into more issues. Also make sure the dual motherboard you get is the latest revision without any AGP or PCI problems.

Currently we have an Elektra inside a Tyan Tiger MP rev3 system with dual Athlon MPs, and we are getting great PCI performance and no issues to report at this time. We did have problems with the Tyan Tiger MP Rev1, so buyer beware.
I suspect I'll edit this post every so often to keep it up to date. Also if you have any of the mentioned untested motherboards (nForce, SiS745), feel free to try the PCI test so we can get a rough idea of how they perform. I'll eventually get a hard number from these, as well, but until then this could help guide us.
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<a href=http://infinitevortex.com>Infinite Vortex Audio</a>
<font size=-1>[ This Message was edited by: subhuman on 2002-01-23 09:43 ]</font>
<font size=-1>[ This Message was edited by: subhuman on 2002-01-23 09:45 ]</font>