What internal parts of the IR3 restrict it from shooting at 20 bps exactly? Because I shoot mine quite regularly at 17, and I've seen plenty of people who've maxed 'em out. Maybe my internals are just special, but they don't seem to have any trouble handling the job. The IR3 will shoot to it's board limit just fine, and if the board were less restricted, it'd be capable of shooting beyond that.
The IR3 is lighter and smaller than the LCD and LED. It's got the Space Frame, COPS (which works far better than any IR "eyes", don't let anyone tell you otherwise), redesigned LCD display and the opto switch. The only difference between it and the Speed is that the Speed has no LCD screen, and has some higher flow parts (redesigned LPR, internal body mods, higher flow valve and bolt) allowing it to operate at a couple hundred PSI less than the IR3. The LCD lacks the space frame, which strange as it may look, is very comfortable to use, it uses a microswitch board (mem 4 and up on the IR3's do not), it has a longer body because of it's larger solenoid, and doesn't have an anti chop system. The LED is pretty basic compared to the LCD and beyond. It's got a monstrous solenoid, it's heavier, obviously no LCD board, it's bolt is shorter, it came stock with a single trigger, so most of the ones with doubles are hack jobs with an aftermarket trigger guard bolted on, and it's pretty much unmilled (there are some versions with slight milling, but in the LED, the entire back half behind the roto breach cannot be milled at all). The new A4 looks pretty nice (all except for the "improved" trigger), kind of like the love child of the Speed and IR3. It operates at pressures like the Speed, is shorter and lighter than the IR3, has the "soft touch" bolt, new twist lock feedneck, and a useless guage. But those are obviously going to go for more money for a while.