I felt the imaging was a bit better and the bass was better as well.
With the newer type pads I felt my ears were rubbing against the grilles covering the drivers and I couldn't angle the cups enough with the newer arc so the end result was a weird fit. Maybe it is only me with this problem but I prefer the older arc in that respect. Oddly enough I didn't feel that with the leather pads so it was comfy even with the new arc, the pads adjusted to the shape much better.
There is also the option of real leather earpads (like on SR-404LE and SR-507), they worked far better for me than the pleather ones and at the same time improved the sound so they might worth the extra money (ymmv of course). I didn't like the newer version of the pleather pads and the newer arcs only worked with the leather pads for me as I couldn't get enought angle movement.
That's a nice price, although I like the idea of Sandy Bridge more as is a lot more efficient (the TDP is misleading, in reality it is more efficient) and has a decent built-in GPU as well and in this configuration it has four cores, not two.
Damn, why I don't live in the US, I would buy this laptop if I could, Quad-core Sandy Bridge CPU, ATI GPU (switchable), etc etc...
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Yes, switching to a Halide Bridge made a big difference to the overall sound even if the amp I use is a temporary solution.
It especially matters with something like an O2 MK1 717 combination, a good DAC is not enough.