Thanks for the advice Easyrider and LongEZDaveA.
I realise the retractable main gear is probably not the most sensible or practical option! I believe Rutan estimated the speed increase at 12-14kt, with the obvious disadvantages of complexity, cost, weight and reduced fuel. Looks good though!
No, I'm not a carbon fibre expert, but know enough to realise that it is not a simple swap. Frankly, I'll have all on convincing the UK LAA to let me install the ULPower engine, let alone fit a retractable gear or use a different material. This is something which I will need to consider very carefully.
As for the CS prop, I've always believed that the only reason people use fixed pitch props is because they don't want to spend the money. I had the disadvantages of a poorly suited prop shown to me early on - my first training aircraft would cruise at 100kt on 50% power (7gph) or, alternatively, 100kt on 100% (14gph)! Climbed well though... But would have been so much more aircraft with a CS prop. I suppose that has prejudiced me against fixed pitch.
Anyway, thanks for the advice.