Just use multiple pumps. There are very few ways to pump lava (three blocks, I believe), none of which can be sped up in any way other than using many at once.
An important caveat, though: the faster you pump lava, the more lava flow block recalculations have to be done each tick and the more lag it causes, so there's a point where "fast" becomes "unplayably slow". When exactly you reach the point of negative returns (in terms of real-world speed and slideshow frame rates) will vary with the power of the machine running the server portion of the game. If you're playing multiplayer? This will almost certainly kill the server and get you a stern talking to / banning from the admins.