What HW / OS is recommeded

Hi,
we are planning to upgrade our servers but deciding on the right 
configuration seems to be quite difficult.

As for the system. About 50 tables, 20M records and growing about 
500k-1m per month.
The systems mostly loads data from files (perl batch jobs). And 
generates client files. Jobs generally dont run at the same time, but 
timely loading/delivery is very important. We also run tomcat with no 
more than 5-10 concurrent users connecting. (mostly browsing data)

We are currently looking at Dell / HP
but the questions is

- how many processors (2 or 4)
- do we gain with 4 cpus if we probably never have a few users connected
- what processors are recommended  Opteron / Xeon / Itanium
- how much memory ?  2GB ? 4GB ?
- Disks, i guess we go with Raid5, 15k SCSI
- what OS ? Suse / RHE3 / Fedora /
- Disk controller ?


Currently we run it on a Dell Blade, dual P3 1.4ghz with 1G memory
Adding 1GB memory did actually not bring much performance gains.

Does anyone have some first hand experience? Can anybody point me to 
some resources ? Or recommend certain systems?
What kind of performance gain can be expected going from a P3 to a 
higher end processor ? 

Thanks for any suggestions

Alex