Bonded ethernet speed

Question

A little background: we're a small post production facility that's got a mix of Mac and Windows machines. We recently set up a 12TB NAS on our network, with the intention of capturing uncompressed Standard Def video and ProRes-compressed HD video directly to the shared storage.
I have a friend who works for a major internet CDN as a network engineer, and he's been advising me on upgrading the network. We decided to go with bonded ethernet on all of the critical machines rather than Fibre Channel, for cost reasons. He recommended a Cisco managed switch (SG300-28), which I got. He came over a few nights ago and we rewired everything and got stuff set up. The issue we're seeing is that we had expected to see approximately double our previous bandwidth. What we're getting is a slight improvement over the speed we saw on the old unmanaged DLink switch using non-bonded ethernet.
We've set up Jumbo Packets on the Cisco Switch, and he fiddled with the bonded ethernet settings in netstat on one of our MacPros so that it's also using jumbo packets. The NAS is Linux Based (OpenFiler), with an 8-drive RAID-6 array, and a dual-port Intel Pro/1000 NIC, also Bonded and set for jumbo packets.
Basically, we're getting a couple megaBYTES per second more than we were before - somewhere around 60-75 on average, whether the mac is talking to another PC or to the NAS. We do occasionally see bursts up to 110MB/S (that's Bytes), but I would expect that with the bonded connection we should see more like 120-140 (128 is the theoretical max for a single ethernet, which I don't really expect. I'd be happy if we could do 120-140 steadily). We're not even getting peaks near that, let alone sustained rates.
To test, I'm using the Blackmagic Disk Speed Utility, which will generate a temp video file on the fly and write it to the target drive, so the speed of the drives on the MacPro are not a factor - the Disk Speed Utility is merely writing to the target drive (one on the network), and then reading from it. It reports its rates in MB/s, and frames per second at various resolutions, and we're also watching on the Activity Monitor's network tab. They're showing the same speed, between 60-75MB/s, which is easily enough for standard definition. But I'd like to see more speed for dealing with large file copies.
Any ideas? do we need to get a better NIC for the mac?

Answer 1

ok, so I guess the best we can hope for is in the 60-75MB range then? that's disappointing.
I guess it does make sense, though, to throw one of the dual-nic cards we bought for a PC that already has gigabit onboard into the NAS box, to have 4 ports bonded there, based on what you guys are saying. That way we'd have 4 separate 1-gb pipes to the shared storage, which should allow us to play back 2-3 streams of video to multiple machines off the same drive (the drive speed should be more than enough to handle this. In my experience, a setup like this should be capable of 400+MB/second, easily, so the RAID won't be a bottleneck). Hmm. I guess that's not all bad.
Thanks!