Yeah, you will find most V5s will come with a high spec list as they where a sort of "highline" model. Early V5 models came with 150BHP but most will be 170BHP, fuel economy is shocking for the sort of performance you get. A 1.8T with a remap will leave a V5 for dust, do considerably better MPG and I'd hazard an estimated guess that they will cost less to buy in the first place (granted it probably wont be as high a spec). Depends what your after in the MK4 really.
If you want a nice nippy sporty hatchback the 1.8T is the way forward.
If you want a highspecd to do motorway miles in a GT TDI 150 is the way forward.
If you want a high spec thats quick then the 2.8 V6 is worth a look.
You will find some 1.8Ts with lots of toys but will be considerably harder to find as the V engine range of models you will find will more often than not come with a nice spec, as well as the 150 dervs.