I've been working on spinning more through the winter and now am quite comfortable at 100. I go as high as 115 or so before I start moving around too much (bouncing).
Spinning fast isn't the end all, just another thing you can do -- my experience is that when I spin more my heart rate climbs more and faster and when I mash more my HR goes up less, but my legs burn more and take longer to recover/get back up to speed. I recently got a Garmin 305 that records speed, HR, cadence, grade, elevation and more... very helpful in analyzing what's working and what isn't.
..been mixing the two and trying to be able to recover faster from either.