I am planning to use virtual machines, build a lot of C++ projects and work with signal processing, and don't plan to overclock (even if it is very simple with 2500K). Which CPU among these should i choose? The Xeon E3 gives HT, 2MB cache and new core architecture - Ivy Bridge. May i feel the difference, assuming that i do not plan to use Xeon's VT-d technology and don't plan to overclock 2500K? The motherboard will be ASRock H77 Pro4/MVP (H77 - no OC) - i found that it tested with this Xeon E3. Sorry for poor english, hello from Russia
Hyperthreading would probably provide at least a moderate benefit when it comes to compiling the code you write. Whether or not that would be enough to justify the added cost is something you'll have to decide. Hyperthreading, at least in theory, would allow you to be compiling two source files, at the same time, on the same CPU core. It's not quite that simple, but you might be able to get a 10-20% across the board performance boost when compiling, and it might also provide a similar performance benefit to the VMs. Nothing spectacular, but still significant.
An SSD will help you more than anything with compiling as files are accessed rapid fire. My Core2Quad compiles pretty well on my laptop. I/O is still king. I know this comment has nothing to do with CPUs but if you're talking about compiling getting those files to the compiler process will be tantamount to loading bullets in a gun rather than the muzzle velocity of one firearm versus another. Most multi-core CPUs will do okay with the actual compile.