When is it required to get a quad for rendering?

im thinking of getting back into graphics design - mainly photoshop and flash. when do you think it is actually necessary to purchase a decent p2/i7 box for this? i know if i keep my wolfdale overclocked it will pump out enough for games... but i would also like to be back into design full time for the rest of the summer. i am debating if i should get a macbook or build a new quad core bawx. ideas/thoughts? time difference between my wolfdale and a p2 granted i would overclock both to the max potential?

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If you use photoshop mainly, then you can use your wolfdale for longer...
Reason - The PS wont show very high difference between a Quad and dual as it is more of Clock speed dependent...

But for other apps, the Quad would surely be best suited...

So like wisecracker said, add more RAM as PS now can utilize more than 4GB of RAM ( Provided it runs on a 64-bit OS) and fasterizing the disk I/O would give a little improvement in I/O performance as it reduces the access time...

But if you want to make a purchase, then wait till September if you are not in a hurry as newer CPUs will be available, resulting in reduction of prices of the current CPUs...