Unfortunately the engine lets it down, even the 2.8i isn't fast, I had a xr4i, bored to 2.9 fitted with a warmer cam modded heads, and it was still slower than my 2.1PINTO AUTOMATIC by a long way, and a lot thirstier.
In the long run decide how much power you want, there are obvious things like engine transplants such as cossie, pinto, zetec, duratec etc, as the V6 does not lend itself very well to tuning.
If sticking with the V6 however it defo needs a warmer cam, and a different carb, such as a 40DFI, but very hard to get hold of, so most go for a 38DGAS.
Because of the siamese ports the headwork can be extremely effective on these engines when combined with carb/exhaust/air filter etc.
Some people have even cossie powered them, or V8, my dads xr4i runs a 4 litre rover V8, goes in a treat.
tabetha