So I just tested some things; it turns out that the behavior of autarchic gates has been changed a bit. With one energy pulser active, they seem to choose between extracting one and two items at random; multiple pulsers do still appear to double that, up to four. More than four active pulsers seem to have no effect; anywhere from four to eight will empty a stack of 64 items in about five pulses. So diamond gates really don't have any advantage over gold gates in that respect.
Higher-powered engines do still increase the number of items pulled. The Creative Engine is the only one I've tested that can pull more than sixteen items at once; it pulls half a stack. A hot industrial steam engine can pull 16 items at once, but will eventually overheat. Testing of the commercial engine is in progress.
Update: Turns out that none of the Railcraft engines ever actually overheat when they're powering a wooden pipe. They heat up to the red stage (and the more powerful engines do so more quickly); but stabilize at some point and stop gaining RF. All of them (Hobbyist, Commercial, and Industrial) actually move items at the same rate, despite their differing steam consumption and energy production rates: sixteen at a time when fully heated.