For an actuator, 2.8cm/s is a pretty decent speed. I've got one that moves at 3.5mm/s, so by comparison, I'd be happy with 2.8cm/s. If the actuator is quite highly rated force-wise, you could configure your system with a ratio in such a way that the lifter moves a large degree for a relatively small movement of the actuator.

If you want something much faster but still want a high level of force, you're gonna be looking at lots of £££ on an extremely high-quality actuator, or custom-built system. The time Nick mentions of ~1 sec isn't really viable with off-the-shelf actuators. It's certainly achievable for a lifter; Storm 2's lifting arm was devilishly fast for an electric system, but no actuator in sight there - there you're talking about a Magmotor running through a custom-made gearbox setup.

Bear in mind also that your lifter doesn't have to be fast to be effective. If your lifting arm is under a robot and moves, say, about 10-20% of its total travelling distance, the chances are your opponent's wheels will be off the ground and you'll have broken their traction. They're now at your mercy (until you lower your lifter or they fall off) to do with them as you please
So if your lifter takes 10 seconds to go from down to fully up, that doesn't mean it'll take you 10 seconds to lift your opponent up to immobilise them. You could probably manage that in 1-2 seconds