I'm looking for a track bike. Help me decide between the TK2 and TK3.

TK2 $1400

TK3 $800

Aside from 2lbs difference in weight, why would I go for the TK2?

Why do I want a track bike? Just for kicks. I'm a roadie and looking for some variety in my training. I've only ridden at a velodrome a few times and always rented. If/when I ride the velodrome again, I'll probably rent again as it's only $5 and I wont have to travel with a bike. Whatever track bike I get will be ridden outside. It's the bike I'll take to the coffee shop. I'll also use it in alley cat races and for training when I ride with weaker riders or girls. I might use it in a flat sprint distance triathlon, especially if I do a double header and ride my TT bike on the Olympic Distance tri on the day before the sprint.

On another note, if I decide on the TK2, why would I pick it over something like the Jamis Sonik?