How do you work out what server spec you need?

It seems like you have to know a bit about everything these days to get up and running. Unfortunately I don't :) Specifically, I'm taking about servers. I recently started receiving pubsub data feed from etsy. It averages around 250 notifications per minute. But obviously, when the USA wakes up that spikes quite heavily. I want to be able to deal with those spikes (about 3 per day) but the rest of day is fine. What's the best method of getting the right server configuration. My current approach is to keep upgrading until the server stops dying... next leap is: - Processor: AMD Phenom II X6-1055T HEXA Core - RAM: 4GB DDR2 SDRAM - HD1: SATA Drive (7,200 rpm) (+500 GB 7200 RPM SATA hard drive) - HD2: SATA Backup Drive (+500 GB SATA (7,200 rpm)) - OS: Linux OS (+CentOS 5 64-bit) - Bandwidth: 6000GB Monthly Transfer (3000 in + 3000 out) (+100M uplink port) Is there a better approach?