Installation: you can get away with a 55-60 tank but don't expect to go far if you put your foot don a few times. you're better off fitting a multi tank setup by removing the spare tyre and using the space for 2-3 small tanks (approx 15). This will decrease your range dramaticall BUT you will be able to use the boot space and your vehicle will not suffer the burden of carrying excesive weight (3 small tanks are only a little heavier than a spare tyre so no mods will need to be done to the suspension).
Economy: not much benefit of you drive it less than 50-75km a day.
Performance: not much difference if you have it tuned correctly (for performance) but you will lose alot of range. however if you have it tuned for range than you will have pathetic performance (it will behave as if it has a 1.6L engine)