righ my xr2i 16v has top speed of 130mph on the clock at 7k rpm

i want a gear box that has longer ratios tbh as it'll be better for on the motorway and also am plannin on going for more poer and don't wan to have a badly noticable limi to top end

whats the diffrences between the rs1800 gearbox and th 2i one and anything else that could be used ?