After being inundated with replies I thought I'd update this for anyone else in the same boat.
There's a 6.6V LiFe pack that fits in the same space as a 4xAA square pack perfectly, so it's now running that.
Diffs were done to 7k/10k/7k as I didn't have any 3k to hand, and it drives SO much better now. They were all grease filled from the factory.
A set of pre-mounted Schuey spikes has increased the track by 5mm, again making handling better, and sitting at the same track as a mate's Losi 8ight now.
Not got round to trying different fuel yet but it's next on the list.
