The Question , the one followed by the question mark..? .is answered , although the information provided was insufficient to provide meaningful advice....although you also agree the quad is the way to go.
Maybe you should also ask what this person wants to do , with what and how , and you can even help
the ones who are compelled to to tell us how much they know , rather than seeking to understand before being understood ....fellow seeker.

I guess it was assumed that since the original message stated that uvbnskoold is using their computer to "... compose music using Logic Studio and all included sounds, VSTs and a lot of different libraries (EW/QL samples) with very little live recording." there was no need to delve further. I don't think anyone on this forum takes the stance of "Let me show you how much I know" and instead actually attempt to answer the questions posed as best as possible.

The primary root issue at hand in the original post was "... I'm torn as to processor." All other decisions seemed to have been made based upon the initial post. From reading back over the entire thread, that specific question was specifically addressed with everyone stating "get the quad core if you can afford it". Including your response to the question.

Everyone offers up their time, their energy and their knowledge and opinion to each other, but unless you sit with someone and do a feasibility and ROI analysis there is no other way to provide a rock solid response for someone else's purchase. In the end, via a forum, it is an opinion, only.

peace.

Mind that for now the iMac 27" has a CPU leak issue (some power is drained in a mysterious way…) typically, it should be corrected someday with an EFI update as it seems rather low level. So don't expect full power from it in the at least coming weeks. (source hardmac, should be online soon, saw it on the French version)

Hey guys, we have always said since the "should i get X now or wait for Y in a couple of months" to purchase now ONLY if you NEED it otherwise why not wait? The great thing is that you could always purchase now and resell it although that is a hassle for me at least. I am quite happy with my 2 year old Mac Pro and all of my 32bit plugs work fine but when idle the Audio Bridge will crash every now and again.... Sorry, tangent. Anyway, I say you wait for the quad core but the lack of internal drives makes me hesitant to use one for music or video but thats because i am stuck in the 'old' way of thinking that reading and writing to an external isn't as reliable as an internal drive but that could be, like i said, an old wives tale at this point. Does the 27" iMac come with only 1 firewire port? Guess you can always daisy chain those if you needed more. Anyway, hope my .02 cents helped to confuse matters worse, kidding. Like i said at the beginning though, get it when you NEED it.

Viva La Panda!