i've also found that in most vehicles that i've driven a massive increase in speed/power can be gained by simply dropping the lever on the left of the drivers compartment to its lowest position, many times i've noticed a speed increase well in excess of 90mph using this technique
here ,http://www.realsteel.co.uk/. snot hard yer know just type in "tuning rover v8" in yer search box and yer get more hits than yer could shake a stick at
it's an increase "of" in a series, but you could try filling your tyres with helium to reduce the weight and smear yer bonnet in baby oil to reduce the friction