Chim engine size

[Marcob]

I've had the Chim bug for while now and will be investing in one soon (in fact it will be my first ever TVR and I can't wait!).
I am strongly leaning towards a 4.5 because it seems to be the "best of both worlds" ie performance and fuel consumption.....but could be tempted into going for a 5l (I went to a dealer and was strongly encouraged not to go for a 5l......surprise surprise he had no 5l to sell!).
Can anyone give me performance and fuel consumption comparisons between these two engine sizes? Other advice would be greatly appreciated!!

Marco