G'day champ,
I also have an ARC top mount installed and have an RC ST185 intercooler system sitting in my shed, so i hope i can help a bit.
I would suggest getting after market parts or custom made parts, like a double row heat exchanger....nothing could help you keep temps down more than double row radiator.......while the stock system can dissipate the heat at stock boost levels, once you start turning up the boost and driving like that for long periods of time you will notice the temps dont drop fast enough (assuming your smart enough to wire in a water temp gauge)
With a system that has an increased internal volume a larger intercooler water pump is a must. Its all about pressure and flow......just keeping stock pressure/flow rates is fine for stock parts/boost but with a double row core your pump will need extra balls to keep the flow rate acceptable.
If you spend a little more money than you think is necessary at the beginning the system will cope with anything you throw at it in the future.....including stop/start city driving with lots of boost in between.....Here in australia its hot all the time, in summer a 40degree day (104f) is normal and the intercooler water temps will skyrocket if the pump isn't running all the time and the core is too small.
Before i got a double row core made i had problems keeping the water temps under 60degrees while sitting at a set of traffic lights...and that's with the pump running constantly..... with a double row core the hottest it runs it 8degrees above ambient...but that is also with 2 small thermo fans helping to move air
The intercooler itself is a robust unit with short internal travel paths, it can hold more boost than most people use for street applications.........pretty much if you treat that baby right, she'll see you through a shit storm