Can I just move the boot drive from my iMac to new Quad G5?

Question

I've "upgraded" from a 1.8 GHz 20" iMac (Rev. A) with 2 GB RAM to a 2.7 GHz Quad G5 with 5 GB RAM and I'm not seeing the performance jump I expected for simple stuff like logging in after system restart (and the start up applications), launching applications, etc. The system profiler reports 4 CPUs, 5 GB RAM, etc. Memory intensive operations seem quicker but I haven't performed any real benchmarks and have a new drive in the iMac. The system just doesn't "feel" faster for basic stuff. I realize these may not be CPU intensive tasks but still expected to see a little more livelier system.
I moved the iMac drive to bay B of the Quad and set it as the boot drive. Are there any folders, caches, etc. that need to be cleared?
The new boot drive (my iMac's old drive) is a 300 GB Seagate ST3300831AS. (The original iMac drive developed a problem and was replaced with this drive a couple of months ago. I noticed an improvement as this drive is a little faster than the stock Maxtor.)
The original Quad drive is a 500 GB Hitachi HDS725050KLA360.
Specs of the two drives seem to be virtually identical as far as I can tell. (Actually I think the Seagate has .5 ms faster seek.)
I'm thinking the issue is that the lack of performance gain I'm seeing is disk I/O and that the iMac wasn't lacking in power for basic stuff so I will only see the performance gain with applications that can take advantage of the additional CPUs and/or GPU. Still, I expected the system to feel a little faster.
I just tried Virtual PC and it didn't seem to start up much faster and I definately expected to see a big improvement with this application.
Any ideas?

Answer 1

That's correct, I moved the iMac drive to the second bay in the new Quad G5.
I wasn't sure if any combination of events would fix this. I didn't think there were any caches or anything else I needed to clear but just posted here to be sure.
The iMac was 10.4.3 and current with all updates. I didn't really think anything was missing but posted here to be sure. My understanding of Mac OS X is such that I was pretty sure that everything the Quad needed was already on the iMac drive. Not that this is necessarily any more reliable, but I asked at the Apple store and they said there was no problem with me moving the drive to the Quad and setting it as the startup volume.
A few people have told me that it's probably OK, but the official method is to use the migration assistant. So today I installed from the Power Mac OS X discs (10.4.2) to the Hitachi drive which I erased, then ran the migration assistant, then software update, then cloned the Hitachi drive back to the Seagate. I think the performace of the two drives is nearly identical (Seagate ST3300831AS, Hitachi HDS725050KLA360) and wanted the smaller (300 GB) Seagate drive to be my main drive.
I've been using Macs for only about a year and have found the experience interesting. On the plus side the performance is fairly consistant and I don't experience progressive system slowdown over a period of months. And of course there are the system update, viruses, etc. issues which are better. On the negative side basic stuff feels faster on a Windows system. I'll try Photoshop which I have no doubt will be faster on the Quad than the iMac and probably faster than a PC, too. But Safari or Firefox don't feel as fast as IE on a new Windows PC. Just my observation. I invested a lot in this Quad and expected to feel a significant speed boost even if it's only for launching applications and displaying web pages. (I have Comcast's highest speed Internet service.)