Cool that you've decided on the 4G, if only for the confirmation bias for myself! is Rob still predicting a June completion for the 4G or will he be posting stuff out earlier?
On the LOD side of things, I have gone for pure silver, which is technically a better conductor than copper (but only marginally and by marginally, only just, but if you want best, it is best). But some people think with silver cables, there is too much treble perhaps after being used to copper, that is also why some LOD manufacturers have started using this "Mundorf Gold", which is silver mixed with 1% Gold (with gold actually being a vastly inferior conductor, it has worse conductivity to zinc and is not normally used for wiring) to take the edge off and make the sound more treble light and supposedly warmer sound.
In my view, silver plated copper is just default, as in, its just standard wire that exists commonly in the industry and the silver is there to prevent oxidisation, whilst some use this layer of silver as a marketing ploy. If you want a premium copper LOD, you could look at the stuff that's been cryoed but you will be paying for it and there's been very little fact based research into whether there is a significant audio difference from normal ultra pure copper to one that's been cryoed. ALO Audio do a pure cryoed copper cable for $85 (not including delivery).
But really what you are comparing is say a decent default LOD out of copper like a FiiO L3/ L9 for $15 and a silver one for $50-60.
Also, do be aware that LODs which work with old gen ipods may not work with new itouches/iphones, make sure they are using the new pin layout in their connectors.