my car is the 130 tdi on an 04 plate and it actually £155 a year for tax . i have owned both the 130 and the 180 bhp a4's the 2.5 is a couple of unsurance groups higher definately heavier on fuel . in my humble oppinion i think the 130 is the best engine very economical if driven sensibily and bullet proof also a considerable amount cheaper to fix if things do go wrong also two hundred quid could get you a good remap that can get you 170 bhp . but this is only my oppinion
i had a mk4 golf 130 tdi, i loved it, yes the tax is cheap, yes the mpg is great and yes it is virtually bullet proof, but having just bought a a4 cabriolet 2.5 tdi, i gotta say the difference is vast, the 2.5 is so much smoother, i am getting 8-10 mpg less with the 2.5, but i love driving it, its really quiet when on the move. the torque is great as well, i was considering getting it remapped but dont think i am going to bother.
changing things like the cambelt will be dear on a 2.5, near double what the 1.9 would cost.
but i dont regret changing at all, good luck in what ever you choose
The big v6 will still return decent Mpg even when driven really hard. I cannot get mine under 25-27 Mpg and that's on a b5 v6 tdi quattro, with 18" alloys and with a far from standard engine...Whatever you wanna buy, take a long test drive in both... I also had big power petrol engines (still own a golf Mk3 Vr6 with a corado engine just for weekend fun) and they would return shocking Mpg (the golf would return under 9 Mpg when driven hard but it sounds sublime) when booted hard. I found the v6 tdi a decent compromise between power and economy and they respond really well to mods (allmost inexistent aftermarket)...A pd wont tune over 160-165 Bhp whatever the tunner tells you on stock hardware and they will eat clutches fairly quick. I have yet to see a failed clutch on a v6 tdi...