If you are a big multi-tasker. And I mean multiple pro apps at once. CS, Aperture, and whatever else. Then yeah, wait for the Octo.
And even if you are a multitasker, the benefits of a octo might be marginal.
Even if you would run exports on Aperture/Lightroom at the same time as you photoshop, you are fine even
now with a Quad 3.0.
And there is not that much more you can do simultaneously in DTP surroundings!?
The benefits will be much higher in video surroundings,where you can decode,compress,render and edit (or whatever) at the same time.
Or in audio where you can leave applications to do some crunching in the background while you fiddle with other stuff.
Generally in the audio/video genre the processes are longer (tens of minutes or hours) so you have actually time to do some multi-stuff.
In photo, exporting 4 separte batches of 50 images each from Raw to 72mb 16 bit Tiffs takes only few minutes, rest of the time the machine is idle in that area.
The human factor starts to get in the way of productivity here...