Also note that 20-30 isn't the ideal area for server FPS.
a14-a19 it was 30-40 is idea. Over 40 is wasted CPU cycles, under 25 is where you'll start to see things lagging out. (a14 is an estimate, might have been ideal since a10, but I can't recall offhand that far back atm.)
a20 ideal is more like 40-50FPS, and I've had servers running up to 53FPS under peak performance. 30-40 still seems to be "ok" territory as long as you're within supported values. Below 30 and you'll start to see a lot of lag/latency.
Oh, and 6GB RAM is below min spec. Pagefile/Swap needs to be a minimum of 8GB as well. CPU is a bit on the low-end in terms of base clock speed, doesn't multithread well, and has low memory bandwidth. The saving grace for you would be to have a decent storage array, but given the rest of the lineup, I'm inclined to think it's something like a 10k SAS drive at best. Running a VM is just adding another layer of slow, and you're already working with Windows.
Final note, FPS for server clock cycles is probably older than the FPS term for monitors and games. It's used in another computing task that pre-dates gaming, and in networking as well. Kind of like "Lag" was primarily used to describe high network latency, and over the past 20 years has been used by gamers to describe low FPS or a bottlenecked system.