1st-time Hackintosh build feedback thread

Hey all -
Looking for some help building a music-producer friend of mine build a Hackintosh.

His target rig: 12-core Mac Pro
His budget: Make it cheaper than buying a Mac Pro

His ideal MacBook (from Apple's site):

Quote:

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- Two 2.66GHz 6-Core Intel Xeon “Westmere” processors
- 6GB (six 1GB) memory
- 1TB hard drive
- 18x double-layer SuperDrive
- ATI Radeon HD 5770 with 1GB GDDR5
- $4,999.00

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I've built dozens of rigs - including servers - but never anything of this caliber and this would also be my first Hackintosh...

Aside from sourcing these parts, what else do I need to take into consideration?

Can a home-built PC/Hackintosh perform at the level of a store-bought MacPro?
What other suggestions, tips, feedback could you guys give me?

*edit - and I just realized I posted this on the x86 forum.... sorry for the noob question but in order to accomodate that RAM capacity, is there a 64-bit OS from Apple or does the x86 version not have the RAM limitations that Windows does?