If you measure the water temps and the air charge temps, then you will get a good idea as to whether the water is getting too hot to absorb any heat from the inlet air

If the temperatures get close, then you would benefit from more water or a bigger rad

Steven RW from here had a big custom made chargecooler on his S2, he eventually ditched it in favour of a twin cossie setup (lighter and more efficient)

Hope this helps

Neil.