as herebemonsters asked, will this work with a 4th gen? i know they are limited and not many on this thread seem to mod them. but mine has a HD that is slowing down/on its last legs. i have a adapter on order that goes to CF, but if i read it correctly, that draws too much power. are CF to SDXC adapters easier to fined? do they work more reliably than CF?
Replacing the HD of a 4th gen with a CF or SDXC is not a big deal. I have done the HD to CF swap in both a 4th gen and an iPod Photo. No big issues, but a couple of minor caveats... the main one is to watch out for jumper pins (master/slave) that stick up too high. A low-profile jumper and careful use of wire cutters is recommended if yours does.
Using an SDXC-to-CF adapter instead of a CF card should work just fine and is cheaper in larger sizes. The caveat here is that you probably need the larger back from a 40/60GB iPod unless you have one of the newer Type I SDXC-to-CF adapters, otherwise the adapter may be little too thick for the thin back of the 20gb models. Reliability should be the same as using a CF card.
AFAIK, no one has tried an SSD in a 4th Gen Classic. In theory, it should work. In addition to the mSATA adapter and SSD, you would also need an adapter to go from the 50-pin ATA port of the 4thGen to the Zif connector on the mSATA adapter. All this would definitely require the thicker back in order to fit. The big questions would be whether the firmware can recognize above 128gb and if the battery could deal with the SSD.