Its going to be hard to really get going on a hybrid like your Trek 7200. A road bike is much faster and a tri/tt bike is faster. On a hybrid you are probably giving up 2 -3mph to a road bike. The hybrid will be fine to train on during the winter and will be fine for doing a tri just to do one - but in my experience the people I know who do a tri with a hybrid or mtn bike get somewhat frustrated and quickly go out and buy a road bike or tri bike pretty quickly.

Regarding average speeds - it of course depends on the length of the course, temp, hills, wind, etc. I typicaly average 21 - 22mph. That typically puts me between top 1/4 and top 1/3 on the bike. I would say middle of the pack is about 19mph average, give or take a bit.

Realize that you will typically ride the tri faster than your training rides. In the tri there are no stoplights and you'll be working on some adreneline. My runs and bikes are always faster during the tri than during my fast training sessions. There is something about catching and passing people and getting pisd when you get passed.