£4-5k could get you something MUCH better, in my opinion, than a punto.
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MISC1691 seems to have about the same list that I would say, but mine:
audi a3
audi s3
fiesta st
suzuki swift sport (cheap insurance)
golf gti (mk1 to mk4)
golf gti anniversary (mk4)
The above cars are what i've been looking at for the price.
I wouldn't go from a punto to another punto unless you absolutely love the first one so much you want a quicker version.
I do like my punto and am happy with it, but if i had the time again, I would have spent my £4.5k on a cheaper car and had the rest to pay for an increased insurance on something quicker OR I would have bought a tjet. But I wouldn't upgrade from a punto to a punto t-jet.
Making a decision on which car is hard, but if you ring around and see what you can get insured on first you'll be fine.
Ultimately though, £4-5k is a lot of money and in my opinion, can buy much more of a car than a tjet.