Cold air feed is pointless, as the coolant runs round the inlet manifold, so it's one step forward, one step back. Straight through exhaust is meh, but you'll loose out on torque, which these engines don't exactly have lots of, so try keeping one of the cats, or something.
There's no point trying with a 1 litre, unless you're willing to spend big money (more then the car is worth in most cases) so