I haven't seen the Purple+ in person, but from what I hear it's basically the same as the Fiji Purple. As a result, I would think that two Purple+ bulbs would make the tank too pink, unless that's what you like. Most people only recommend one supplimental bulb like this in a 4 or 6 bulb setup.
Thanks i guess i will be the guinea pig for this test, i ordered 2x purple +, 1x blue + and 1x aquablue special so i plan on taking before and after pictures so it is clear to tell the color difference and will rate it on a jolson scale of how much i like them.