^ agree.
I use a titanium powerbook (8yrs old now!) as my main machine every day, and have never run any AV software on it (although I may do in future depending on how OSX malware develops.) I keep all my sensitive personal and business data on it, which I would never consider doing on my PC (I dont trust my PC even for checking my online banking) despite the fact it has on-access scanning running all the time and weekly scheduled deep scanning.
The network of PCs I administer otoh has almost every conceivable method of denying malware - on-access scanning, scheduled multiple deep scanning, domain networking, limited accounts (btw the windows user rights system is a joke if you come from any *nix background), individual firewalls, network firewall, numerous system tweaks etc etc and rigorous user training. Still there is about a 1 in 50 chance of an individual machine getting infected with something per week.
The only way you will get a PC to be as secure overall as a mac is by junking any MS os on it and installing then correctly configuring some *nix flavour on it.
As for buying the Mac Pro - if you can afford it, why not