The Type X's are amazing, we did one in a sound 5.1 SQ Audi S4 and it was very clear...it was on a PDX1000, but still. I've never been very Impressed with the Type R's. The MRP line deffinatly isn't regulated (which means it puts out optimal power no matter what the voltage going into the amp is) A general rule is the less voltage an amplifier can get the less output is created. for example an amp tested at 14.4 volts to make 2000 watts is only drawing 13.6 volts so its only making 1600 watts of true power. Regulated amps are able to create that 2000 watts no matter what the input voltage is, usually down to around 12Volts as JL Audios Regulated slash series is.

Usually I would go by the more regulated CEA standard which says the amp only does 1,500 wattsx1 at 4 ohm. The CEA system is alot more reliable than anything else, but as they said earlier, unless ur holding a true 14.4 volts, it wont even be that much out of the amp.