About the furthest you can row on the Cam (unless you go over Baits Bite to Bottisham) is Baits Bite lock to Jesus Lock; and that seems to have become our regular monday evening practice. Warmup, spin, down to Jesus Lock, steady state to Baits Bite, then a piece back. It is about 5 km I think; Baits Bite to the Motorway bridge must be ~30 strokes, then it was (tonight, slight following wind, rating 24) 530 strokes to Jesus Lock (and a rapid stop to avoid going under the weir). The rowcoach said ~1:55 split average, maybe a little better. We need to learn to take the rating up; the first half was at ~22 or a fraction under; we ended at 28. This is semi-deliberate to settle us down.
Does that fit? 560/24 ~ 23 1/2 mins. 5km (and against the stream) in 23 mins would be over 2:00, so maybe it is more like 5.5 km. Hmm, and if I put the rate at 25 and say only 20 strokes to the Motorway bridge from the lock? Maybe. Next time we should just time it, that would be easier.
Meanwhile, if you want to see a very rough crew do their first bumps start of the year, try http://www.spannerspotter.com/v/specials/drjpstag/post-drjp-stag-night-5.flv.html. The title is a clue. Note that this was the first time 3 had done a bumps start; in fact it was the first time 3 had rated above 30, let alone 35.