Moving to a faster machine does not improve performance

[Stephane Deverly]

We moved a database from a server to a faster one and didn't see any major performance improvement.
We are using mysql 4.018.
We moved from :

Intel(R) Xeon(TM) CPU 2.00GHz *2
cpu MHz : 1993.967
cache size : 256 KB
2 gig of ram
Linux kernel 2.425
network link 100 Mbit
hard disk : ST373405LW Capacity: 73 GB Speed: 10000 rpm Seek time: 5.1 ms avg Interface: Ultra160 SCSI (Up to 160 Mb Per Second)

to :
Intel(R) Xeon(TM) CPU 2.40GHz *2
cpu MHz : 2393.816
cache size : 512 KB
RAM : 6 Gig
Linux version : 2.6.7
HardDisk : ST3146807LC Capacity: 147 GB Speed: 10000 rpm Seek time: 4.7 ms avg Interface: Ultra320 SCSI (Up to 320 Mb Per Second)

My question is : should we expect a major improvment from the move ? We some statistics plotted, and we can see that we never use the cpus at 100%, although we have a load quite high ( 3.0 ).
There is almost no read from the disks. The database seems to be fully cached into memory by the file system. We have some disk writes for the updates.
Is there anything we should check ?
Thanks.