Ok
So I've been doing more testing today. Nothing too intensive (that comes monday when back at work and can get several hours listening in!). I decided to test it with the stock battery still in as that battery mod scares the life out of me. So far I've got about 7-8 hours worth of alac files playing. No crashes, no freezes, no hang ups nothing. Navigation is nice and smooth, no pauses or hard drive whine it's just silent. Odd flicker from the hard drive light but that's about it. It did get slightly warm over 2 hours but that was because I was copying stuff over on to it. Iriver really were ahead of the game when they released this thing way back when. I'm just glad I never chuck things out and can enjoy it all over again (with thanks to rockbox of course). The other obvious difference is weight. Makes quite a difference swopping the hard drive out.
Any iriver owners thinking about doing this just go ahead and do it. Even an adaptor and card would be the same or more capacity then what you have now anyway. Just one slight regret and that it's not 120 gig space available as that would reflect the name of the player
Cheers
Edit, so the battery crapped out at 9 hours solid charge. Would have made it to 10 but started playing about with navigation and volume. Not bad for the original battery
More than enough for a day at work right now for me.