I asked the cooler to be safe to 600 bhp and 2.5 bar, just to be on the safe side. Prices are around 550. However he is looking into different core options like marstons and hydro flow. I'm going up to see him tomorrow.
The more efficient the core the smaller it needs to be. I get the whole larger surface area bit but if the end tanks don't guide and collect the air well it will just take the path of least resistance.
I'm hoping to get a small efficient cooler taking up minimal space.