I've just installed vmware esx on a relatively cheap but new machine and I put a VM for pfsense to run my firewall and that's running perfectly so far.
I now want to look at shutting down my old ass HP Proliant G4 server which is a dual xeon 3ghz, 2GB ram , 10,000 RPM scsi drive machine and moving everything it was doing to a new VM on this newer hardware
AMD A8-3870K Black APU Quad Core, 8GB ram, 500GB 7200rpm sata.
I planned on dedicating 3 of the 4 cores to the new VM (ubuntu 12.10 server) and 6GB ram.
Am I likely to see a performance decrease or increase? It's difficult to find reviews or articles for this kind of comparison.
You'll probably see at least as much performance out of the VM as the old system (and I'd expect more), but there's a lot of factors at work.
FWIW, I have a Minecraft server running in an Ubuntu VM on ESXi and it runs well. I have another VM running Plex's media server, and it handles transcoding on demand well, too (even HD). That's the most processor-intensive thing I've really thrown at it, though. Most of the other stuff it does doesn't use much processing power. This is on a lowly dual core Core 2 Duo with 8GB RAM.
This. Is is disk/CPU/memory/network intensive? Where are the current bottlenecks?
Only thing meaningful I can say is that we find ESXi to have no meaningful impact on performance, and we're running ~30 VMs on a 24 core box/96Gb of RAM. In particular, the memory/CPU sharing means we've no desire to return to raw hardware (I'd honestly suggest leaving resource undedicated unless you've other hungry VMs on the box that must be constrained).
Only complaint is that vSphere has a rubbish UI and the plugin only supports Win/Lin clients.
TL;DR I suspect you'll /probably/ be happy.
The applications running are generally disk and network intensive.
I went ahead and did it and so far I have notice that if anything performance has increased