I just set up a dual core 2.3 G5 server running here is my unscientific take on the issue:

This is where as a beta test I put a G5 imac up against their existing 1.25 G4 tower. During those tests some things were noticeably slower and some were noticeably faster. From my perspective the G5 dual core is noticeably faster on everything!

According to the Activity monitor, it does not appear that the load from Helix is spread between the cores. However, when Helix wants to take everything, (about 93 -97%) the other core is available and usage seems to spike and fall on the other core frequently. This indicates that there are other processes that require time frequently during normal server operation and the OS appears to be good at getting those processes the time they need on the other core.

This is only a 368 MB collection but an automated run of both utilities with a full machine restart at the end is about a two minute procedure to quit, backup, run both utilities, restart and launch the collection.

My subjective perception (having only used the dual quad with TB2) is that you can definitely tell the difference between the quad and the 2.3 DC. However, personally the 2.3 is very noticeably faster than any other machine I have worked with. If price were no object I am completely blown away by the quad but for a Helix Server I don't know that the extra $800 would have a payback unless you were running several other applications on the server as well.

My subjective opinion is that there is good communication among the cores. I think Helix does it right in that it can be a processor hog on one of the cores. It appears the OS is good at using the other core as needed so it makes a nice system. Of course the quad could be neater with other savvy apps because it would have another 2 cores to spread the load out over. I would be interested to know if some of this comes from 10.4 or if it has something to do with the dual core vs the dual. I don't remember what the dual test said it had for an OS. Could it be that the dual processors would work the same if they were running the same OS?

Even though Activity Monitor said that Helix was grabbing an entire core, I never heard the fans kick in.

I think that the FSB and the SATA on these new machines make for a good improvement in the overall system speed.

Will monitor the RAM situation. It appears that 2 GB is adequate for the 368 MB collection. You really can see this with these systems. The SATA really helps load things and get them started faster than I have been used to but as you start filling the RAM these babies really begin to fly!

I can't tell for sure how much of the document to image rendering performance gains are from Helix 6, the Dual Core, or the fact that the documents are now on the actual Helix Server but images come up much much faster now!

With hundreds of thousands of documents I didn't want to have them on the Helix Server in OS 9. Therefore, I set it up so that the documents were on a 733 MHz G4 running 10.x (10.3.9 at time of conversion). I copied the documents from the G4 to the G5. Brought up a user global form and changed the base path. Presto, instant images served from the G5 instead of the G4. THANK YOU RECOVERY TEAM!!!

The dispatcher couldn't be more thrilled with the new Helix 6 system. However, he was running a 9600 with a 500 MHz g3 upgrade card and OS 9.1. He now has the 1.25 G4 tower and 10.3.9. (By the way, I changed the Mapqest link to a Google maps link and this really makes for a nice system now. Helix builds the link much faster and Google in OS X lets you drag the map around. Very nice.)

The employee that spends all day using the system to bring up customer records and make/answer phone calls, (Mostly searching for a customer record, then clicking various buttons to bring different transaction history lists set by user variable limits.), says she really doesn't notice any difference with the new system!!! Now granted the morning has been crazy there for unrelated reasons but she has been on they system and in her subjective opinion it is about the same as it always has been. Her machine is a G5 iMac (1.8 Rev 2 I think).

My interim conclusion is that a good client with a fast enough graphic card for the OS it is using is perhaps the most important factor in user perceptions. Even going from a G3 400 MHz to a dual quad Helix Server only made a modest perceptual difference to someone using a 1.67 G4 PowerBook as a Client. There is no denying that for RADE, the utilities and launching and saving, these new machines are out of the ballpark faster than what they replace. Very, very nice. I think that the improvements in Helix 6 and the bigger hardware will make itself more noticeable for collections with more connected clients. Unfortunately, my larger client sites haven't upgraded yet.

That's my story and I'm sticking to it ;-) Hope it wasn't a waste of bandwidth. Wanted more specifics but I had to have everything up and running with the new machines setup before the day shift showed up. FWIW, the mini really does make a very nice client.