4 in rollers make speed pretty easy. I ride the 3 in krietlers and find I can easily average about 18-20 mph in my zone. On the road that translates to 16-18 mph.

One thing I recommend to everyone trying rollers is to ride off of them at speed. Once you do, you realize that its not that big a deal and you don't flip out about it anymore. Also, cheap wally world yoga mats help protect carpets from those great black streaks in case you DO fall off.

BTW, I've been riding rollers for 2 winters now, and still have difficulty standing and have not even tried to ride no-handed. Not everyone picks it up so quickly.