There are many, many variables when it comes to growing and keeping Acropora. If you just want to keep some Montipora or Birds Nest, you can get away with 200 par with decent water quality.
If you want to keep Acropora, PAR is only part of the equation. 225 to 250 would be the least I would recommend and this is assuming you have excellent, variable flow. You'll also need to have your nutrients worked out in how you're keeping them stable and at what level.
I run anywhere from 350 to 400 PAR using MH for 6 hours and 12 hours of LEDs, but at varying percentages to compliment the MH. If you want to bump up the PAR to this level, or higher, you'll need to have your Alk, Cal, Mag, Nitrates, Phosphates, and PH very stable and at the optimal levels. Flow is paramount and so are nutrients. The higher the PAR, the higher the nutrients and flow.