I've owned tons of macs, the newest ( and last mac I'll ever buy. Apple no longer makes serious machines ) being a 27in 2011 iMac, good machine, but before you dump yourself into the Apple system, you need to be aware of a few things before you buy.
1: Your buying a machine that it not user upgradeable besides the ram, unless your warranty is already up. Otherwise it voids your warranty.
2: You cannot upgrade your GPU, at all
3: Your stuck with Apple hard drives
4: Your stuck with a machine that will get very loud ( at least mine does ), and runs hot when its under load
5: its also a machine that will not be supported for very long compared to a Nix/Windows machine.
7: You also need to be aware that if anything goes wrong, your stuck with apple customer service, which is not good. And as far as in store support, your pretty much with the " genius ( retard ) " bar. Some people think PC vendors have bad customer service, but that has not been my experience, ever. Then again, I've only ever had 1 major failure on my PCs. ( PSU )
8: Im not saying its not a good machine, it is. But you need to try out out to see if its right for you, the only reason I say that is because macs are very niche market, they arent for everyone, so thats why you should try it out before you buy it.
And as best all in one performance? Try again.
http://www.hp.com/united-states/campaigns/workstations/z1_features.html#.UBdqh6C3j4Y
Right from the mothership.