you can tune your TDI to get some cracking figures and performance. Petrol is the obvious choice for mega figures and performance. Some of the cupra lads are running 300bhp+ safely, with relative inexpensive mods. Remap and exhaust on a cupra alone, and youl get close to 300bhp. TDIs are different, they can give you a good balance. You can get a relatively easy 200bhp / 300lbft with remap but still get 50mpg dependant on driving style.
My 140 is pushing around 220 and 360+lbft with decat, backbox removal, high flow cusom induction and remap to suit. Hybrid turbo and remap will get you more still. Theres a guy on here by the name of devonmikeyboy, Hes got a 140 TDI A3 which is kicking out over 300bhp safely. One thing i will say though, if you go down the performance route, get the work done by reputable people. Same goes for remapping. Dont be tempted for the cheaper option. Thats when the horror stories happen