Ugh...
I'm not sure where you get your information dude.
How is there no need for anti virus? And mac's DO have anti viruses available. Both linux and mac OSs CAN get viruses, if anyone tells you otherwise, they're stupid.
'Fast' meaning? Speed for the most part is based on the computer itself, although the OS does play a part.... But if you look at it like that, every newer OS is quite fast.
And mac OSs aren't $1000... The units themselves sell for that price (and up), but not the actual OS. Computers that come loaded with linux aren't free... And some distributions of linux aren't free.