Seems a bit weird to compare a £20k hatch with a car that easily costs 50% more even 2nd hand. Also seems weird to say you would remap it when you think tuning is a waste of time and money.
Anyway, I would love a 335i. However emissions on them are not great and I think the residuals will take a hit as a result just as every non-green car is.
To be fair, you can make an Ed30 have 320bhp with £1k, which is not far off how much it would cost to remap the heavier 335i.
Like Ben, I would have the 135i before the 335i.
Regarding the Cayman S, in a straight line, I would not say that there would be a significant difference between a Cayman S and an Ed30.
Guess it depends how much you want to sink in to a daily runner. Personally, I will probably get an A4 TDi next time and a toy along the lines of an Escort Cosworth or similar.