M4300 performance issues (incl. VMware)

Work are trying to get me to upgrade from a D610 to M4300.
On paper the M4300 is a lot better but I have my doubts.
- significantly higher resolution screen (but my eyesight is no longer that good)
- 4GB vs 2GB RAM (I really want more memory!)
- 7200 rpm vs 5400 rpm disk
- 120 GB vs 60 GB disk
- 2.5 GHz cpu vs 2.0 GHz
- dual core vs single core cpu
(Both are running Windows XP)

Set against which is the undesireable increase in weight and bulk - will no longer fit in most hotel safes.

The real killer seems to be the performance. For some uses the machine seems a lot slower than the D610 - in particular I am thinking of a corporate application running on Redhat Linux inside VMware. Especially the graphics.
I think I have seen the same on colleague's machines so I don't think it is machine specific and I moved the VM directly from the D610 to the M4300 as it is installed as .vmdk files on a NTFS formatted disk in the drive bay so I can't blame disk fragmentation or performance.

I wonder if anyone has any suggestions? Are there any known issues?