The 1.3 cap is a good upgrade for a cooling system in good working order. It increases the pressure thereby giving you better cooling efficiency.

A lot of ppl have asked the same question as you have, and I would say yes it will perform better.

Some people have said that it will cause their radiator to leak blah blah. A radiator that cannot take 1.3 of pressure had better be replaced.

Cooling mods should always be one for the first mods on a car. In saying that, this will include a bigger radiator, lower temp thermostat, lower temp thermatic switch(or a fan adjustable fan controller) and silicon hoses.

I am really glad you are modding your cooling system, as 4 degC cooler equates to 1 extra hp.

Regards,
Mao