My Testing went like this......

Pro Alloy Custom Cooler - 63mm Core - Single Pass vs GRS Evo 5 50mm Core - Twin Pass

1.9 Bar Boost - Approximately 10°C Ambient Temp.

Pro Alloy - My ACT Gauge couldn't read it (it stops at 70°C).

GRS - 35°C Maximum.

I personally think the RST NEEDS Twin Pass.