MotoGP in Jerez pics and panning question

Went to the MototGP practice session on Friday in Jerez and had a great day as it was my first motorsport event and I had a paddock pass. I dialled in Peter Miller (of Sports Illustrated) custom function settings on the 1D m4 and took a 300mm f2.8 +1.4TC

Below are some of the better shots from the day but I ended up with a large amount of shots which were a tiny bit soft due to my panning skills being poor. Most of the pans between 1/100-1/200sec were not good enough so I had to increase the shutter speed. They looked ok on the lcd and the monitor but when viewed at 100% they were a touch off.

I've seen many awesome motorsport panning shots with a shutter of less than 1/100 sec which leaves me wondering whether the top guys use a monopod or not. I tried it with the 300mm f2.8 but it felt very awkward so I resorted to hand holding it. Can anyone offer me some advice on panning with a big lens? Regards.