What will the web server do? Process complex SQL queries, only retrieve documents, create PDF documents? In other words, are you running web applications that can take advantage of 8 physical cores when 200 users access it? If not, then go for the faster E5640 as it will process single threads faster. Having 2 CPUs won't make the server more reliable. Using RAID, dual Ethernet ports and a UPS is more important. I've never seen a CPU fail in a server; therefore that's the least of my worries.