That old chestnut!
Wrong fuel and poor right foot strength!
I think your colleagues grin just about matched mine!
4.5 is great. I started at 1, went to 4 then cracked a turbo housing so thought at that point I may as we'll go 4.5.
I have loved the route I have taken as I have had a discernible step up for each chunk of money.
I also have the Litchfield suspension, which I adore.
Next step is the front control arms and bbk.
Then more power, if I can get round to it.
If you have the budget for 4.5 I'd certainly do it. Although I'd have a chat with Iain and see if you can utilise a different (more expensive) turbo that you will be able to use in a later stage as well. This way you don't have to sell the turbo to move onward and upward.