Interesting that brewing IPAs with RO was mentioned. John Palmer and I visited a brewery in Indy yesterday and all they use is RO water....and nothing else. No minerals, no acids, nothing.
On top of that, they have been monitoring their mash pH and it was at 5.4. However, they were performing that measurement at mash temp! Needless to say, the true (room temp) pH was a bit higher than that. Both John and I could detect a slight tannic bit, but it wasn't too bad.
Needless to say, we recommended that they at least bring the calcium content up to help lower the mash pH and supply that needed ion. I mentioned that story about my trial of using 100 ppm sulfate and its lack of hop character and my preference of using 300 ppm. Ultimately, John suggested that 200 ppm is a good starting point. I think that is an appropriate starting point for any pale ale brewer. Take it higher when you are ready.
PS: that brewer's pH meter had recently been thrown away. The probe's bulb had broken. I wonder why? ;-D