My point about that in general is that if you are testing out a 4CPU Intel machine and it doesn't do the job, then it's hard to get any bigger. If you were testing a 4CPU Sun machine and it didn't do the job, it's easy to buy a bigger one that wouldn't require any difference in your app.

In my experience it is almost always more cost effective to design your app from the outset to work in a web farm enviroment and then when your 4 proc box runs out of steam start adding more 4 proc servers. The cost of flash hardware doesn't tend to scale linearly.

It does mean you need to invest in a hardware load balancing switch to do it properly though.