Alternator output will be determined by the regulator. Regardless of the alternator manufacturer, the output of the alternator is dependent on the load it senses. Most Subaru alternators peak at 90 amps on the smaller engine models. Trial and error will tell. How many amps do you expect to draw and for how long?
Short term usage of high amperage draw will not damage the alternator. You could also up the CCA of the battery in your car and this will lessen the load on the alternator. Install a 750-850 CCA battery and add a 4 gauge ground cable from the battery to the block. I run a 750 in my VDC and there is a lot of electrical load in the car, engine, trans, lights, etc. I have 2 extra ground cables, one to the block, one to the firewall. (Added the firewall cable after I installed the upgraded stereo system to help with the amperage flow to the amplifier mounted in the rear storage area.) Still using the original alternator. It just won't die.