[GSixZero]

I'm thinking about getting a new 27" iMac, and am curious about the performance difference between the dual i3 3.2Ghz, quad i5 2.8Ghz and the quad 2.93 i7Ghz.

What kind of applications will I see real performance bumps from dual to quad procs, as well as the differences between i3, i5, and i7?

Are there situations where the faster dual i3 will out perform the slower quad 2.8? How do I know if it's worth the increase in cost?

I do a lot of work in flash and photoshop, but it's not generally pegging the procs, mostly just flat web work.

For reference, I do my work now on a 2.4 Ghz Core 2 duo MacBook Pro with 4GB of Ram.

[P]

Originally Posted by GSixZero 

I'm thinking about getting a new 27" iMac, and am curious about the performance difference between the dual i3 3.2Ghz, quad i5 2.8Ghz and the quad 2.93 i7Ghz.

Dual i3 to dual i5 - clockspeed only. There is some turbo, but less than you think. Dual i5 to quad i5 - huge (more than double). Quad i5 to quad i7 - clockspeed plus 20%. All of these are raw CPU performance percentages, not complete system, and averaged over workloads.

Originally Posted by GSixZero 

What kind of applications will I see real performance bumps from dual to quad procs, as well as the differences between i3, i5, and i7?

CPU-intensive operations are where the differences are. Things like video encoding are way faster, but Photoshop filters etc are helped as well.

Originally Posted by GSixZero 

Are there situations where the faster dual i3 will out perform the slower quad 2.8?

No.

Actually let me qualify that slightly: The duals have special instructions for encryption that quads get with the next update. Apple doesn't make use of those instructions yet, but they might some day, so there might be a day that some operations go faster on the i3. We're not there yet, and the quad might still be enough faster to compensate.

If your worry is the clockspeed, Intel has that covered. There is something called turbo, which means that the CPU will detect when only a few cores are in use, disable all the other cores and up the clockspeed for the ones that have work to do. The quadcore i5 boosts 4 "bins" when only 2 cores are active. One bin is 133 MHz, so the quad i5 gets 2.8 GHz + 4*133 MHz = 3.33 GHz, more than the i3 dual at 3.2 GHz. The quad has a few other tricks up its sleeve, like a bigger cache and the all important integrated memory controller, so it would be faster anyway, but even neglecting that that i5 quad would be faster.

Originally Posted by GSixZero 

How do I know if it's worth the increase in cost?

I do a lot of work in flash and photoshop, but it's not generally pegging the procs, mostly just flat web work.

For reference, I do my work now on a 2.4 Ghz Core 2 duo MacBook Pro with 4GB of Ram.

Then anything you get will be way faster. If I were you, I would buy the quadcore i5. The next generation that Intel is pushing out right after Christmas looks a lot like that architechture, so I think it's a fair bet that Apple and everyone else will be optimizing for it.

[GSixZero]

Wow, great reply. Thank you.

I guess the last question is whether now is a good time to invest in an iMac. I know that there's always something better around the corner, but are we on the verge of a new architecture or such that makes now a less-good time to buy?

[P]

There is a new architechture on its way, yes, and it will be here somewhere this spring. For the quadcore desktops, the change isn't huge. The biggest change is that the clockspeeds go up quite a bit - the i5 quad will run at 3.3 GHz - and the addition of some new vector instructions that might be important several years down the line. For the duals, the change is bigger as they finally get the integrated memory controller, and for laptops its bigger yet as much of the improvement is in power efficiency. It's at least 4 months to wait though.