On board vs NIC doesn't make any real difference that you are going to see in everyday home use. Everybody uses onboard because it's just not worth it to buy a NIC when the onboard is just as good. There are some reasons to use a NIC, somethimes bleeding-edge gamers will use a NIC as to take the processing load off the CPU, this might get them another frame or two and increase their ping rate slightly and result in less lag. In the server world there advantages to more advanced NICS too. But over 99% of home users will never see the difference between a NIC and onboard LAN. What's built into you're motherboard will work great for you.
Related side note:
I think the Killer NIC that sells for $300 is funny, who's going to spend $300 on a NIC?
Modern on-board NICs typically perform significantly better than add-on NICs going through PCI. However, for average single drive file transfers (around 30 MB/s), it doesn't matter much if at all. When you get into fast (newer, unfragmented, not full) drives and RAID arrays, you tend to notice the performance difference.
There are some on-board NICs which are bridged via the PCI bus, but this is an inferior design which is hopefully disappearing, esp. with the deployment of PCIe.
Using a PCI NIC and a PCI storage controller will of course compound the problem further.
There are other factors to consider -- esp. the CPU overhead of a particular NIC/chipset, but this can be mitigated with the very fast modern CPU's to some degree. Jumbo frames can also help with the PCI issue, but this is hard to set up.
Well first off. It wont load much off the cpu, seeing how it takes like 1% cpu usage, if that. While the windows gui can take up to 10%.Onboard nic's themselves actually sometimes will perform a little bit worse than the onboard connections. Thats because some of the onboard connections are even rated at a pci-e transfer rate. Unless you are going to get a nic thats pci-e than you are out of luck. The only thing that could possibly make the killernic worth buying is that it supposable ignores the tcpstack in windows. Which microsoft claims is something that is improved in vista. Making it redundant to get the killernic. That is if you were willing to pay $300 for a gigabit nic.And who would buy it if it didnt cost $300. Its the illusion that you get what you pay for. The killernic is a known scam and is a complete waste of money. And it makes me laugh when people buy it when i can get lower pings with my onboard lan. Nuff said.
I might point-out this... most people don't know if their motherboards have pci or pcie x1 gigabit LAN, and there are brand new boards that are pci. If concerned, a rosewill rc-401 or Broadcom 5721 will illustrate. Not more than $25, and needs a pcie 1x slot... (Find that in an mATX board... what... its covered by graphics card?)
IF chipset is 8110 its pci and your LAME, but 8111b is pci-e golden. I think the rosewill uses EDIT==> Agere 1310.
==> update: the Agere chipset is now part of LSI and is still listed on LSI website. Both newegg and chiefvalue are OOS of the rosewill. T.D. has Intel 9300 chioset as the PRO/1000 PT for $10 more but is card only.
Anyone that has any form of 'marvell under Vista' problems (NVIDIA guys this means you!) and/or an 8110 MoBo chipset, SHOULD consider the purchase of either the rosewill or the intel for POM.
Onboard LOM versus NIC performance-wise depends on what generation of part you're talking about. It can be a bit complicated if you get all the details.
The bottom line is that the latest NICs have the same performance as the latest LOM solutions, in most cases it's the same silicon and same drivers. If you have a NIC laying around it's more likely to be standard PCI and it's performance is more likely to be lower than a new LOM solution. PCIe is pretty new from a Si perspective so most PCIe NICs are as efficent as LOM.
Newer Ethernet silicon tends to implement more hardware offloads from the TCP or driver stack in the OS and are usually faster or use fewer CPU cycles to hit wire speed (this is true for most of the major vendodrs, I don't know about 3rd tier vendors because I tend to avoid their products).