I bought a Garmin GSC10 cadence meter. It synced with my Timex Global Trainer flawless-ly. I only had to set the wheelsize, which I forgot on the 1st ride out and luckily the speed indicator was so horrible, that I knew there was a problem. Small change and now it works great.
Yesterday after work I took it for its 1st major test ride to see. I headed out to Tulln on a 57km loop. Going there I had a nice back wind. Was able to keep the cadence at a good rate between 75 and 80. Managed speeds between 35-38km/h.
On the way back I slowed down into the head wind. However I felt I hit the sweet spot, by keeping it at a 76-78 cadence. This gave me a good 31km/h which I can maintain.
I am afraid my heartrate strap is either faulty or tripping (hope the last one) but I would have loved to match it against those.