My guess would be 2, but possibly 3 depending on your host computer.
Since UAD plugins put a small load on the host CPU, and more for certain systems (G5's running panther for example) it's not quite an exact science.
The good news is that with the new project pak selling for just $399 or thereabouts, it's one of the best plugin bargains going in my opinion. Providing it works for you of course -- some people have had weird config problems. Me, I'm psyched to get a second card.
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"If it ain't broke, add more plugins"
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