Upgrading from macbook white to imac...which one?

Question

Im looking to upgrade from my macbook white (nearly 2 and a half years old now) to a new imac.
Spec: 2.1 ghz intel core duo, 4gb ram, 120 gb hard drive, 500gb external seagate HD, 160gb external seagate HD
I am running logic 8 and use AU's such as all the native instruments ones, Rob Papen synths and Spectrasonics instruments a lot (normally running at least 10 instances of each in a project). Everything i do is software based and i am not currently running an external audio interface but i will probably get one to connect my mackies and my decks.
My macbook is now struggling to keep up with it all and regularly cuts out while playing which gets very frustrating, therefore i feel it is time to upgrade.
I dont have much money and am looking at buying the basic imac available on the apple site. Would the step up from 2.1ghz dual core to 3.06 ghz i3 processor be significant and very noticable i.e. would it stop logic cutting out while playing? or is it actually worth going for a quad core even though the i3 processor can run 4 threads at once?
Also, is it worth going all out on 8gb of ram or would it not be worth it if i wasnt running a much more powerful processor?
Any issues with the hard drive, graphics cards etc?
Obviously a new imac will have a significantly improved performance to a 2 and half year old basic macbook white but i just need to know if it is worth spending a lot more money on a more top spec imac since i cannot afford to be upgrading very often.
Matt

Answer 1

Even the lowest end base model iMac would be a pretty significant jump from what you have now. The amount of RAM would be the same, but the RAM in your laptop is almost certainly DDR2, while the new system would be DDR3-1333, and the Core i3 has an integrated memory controller which further reduces memory latency. Add to that hyperthreading, and I believe even Turbo Boost, it will make for a very nice step up.
What I would suggest doing, is trying things out with 4GB of RAM and see how it goes for say a month. If after some sufficient period of time, like a month or at least a couple weeks, you need more RAM, it's a lot cheaper to add it aftermarket. Any DDR3-1333 (Non-ECC) SO-DIMM should work. All you need is a Philips #2 screwdriver to remove a couple (captive) screws on the panel on the bottom edge of the system. There are 4 memory banks there you can fill. I want to think the current iMacs can take up to 32GB of RAM in a 4x8GB config.
You might want to consider scraping together just a little extra money for the i5 model however. Long term, it's going to provide better performance. Four physical cores will trump two hyperthreaded cores pretty much any day of the week. There's nothing wrong with the i3, it'll be a big improvement over what you have. However, given what you say you do with your system, the i5 is going to be a significantly better choice if you can find the money.