genrally in these cases it turns out that it would be cheaper just to buy a V8 el in the first place. Even if the costs are close, registration, insurance etc is much cheaper when the car comes from the factory as a v8. You'd definately notice the improvement with the v8, and there are some very simple mods to do to gain more power. However, if you simply want more power (not v8 sound) you could consider a supercharger or turbo kit for the six. very big power figures can be realised in this way.