Sadly, with that budget, you are limited to i3's or an AMD FM2 socket CPU. There aren't any AM3+ mini ITX boards. i3's are faster in games and applications than a stock 750k. Overclocked the 750k/760k could pull ahead slightly in applications, but is still inferior for games. I am unfamiliar with game servers and how much cpu matters for them. If you bump up to a micro ATX build, you could go with an FX 6300, bump it to an FX 6350 and have a better CPU for the same cost as an i3. There are small Micro ATX enclosures that aren't much different in size to an itx.