Herne Hill Velodrome

You shouldn't be spinning out on that gearing at 20mph as you are doing less than 90RPM!
If so you need to work on your cadence by reducing your road gearing to low-mid 60s

You should hit at least 35 mph before spinning out on that gearing.

For the track, most people race the league with about 88-90 GI the sprinters will use 90+

I guess for these sessions Rob would probably want you all to be around the 84-86 mark. Though I may be wrong

http://software.bareknucklebrigade.com/rabbit.applet.html

Sheldon Brown's GI calculator says I have a GI of 78.8 (turns out I didn't count wrong - I am on 48/16)

So if I'm spinning out at, maybe 25mph, what does that mean? I need to work on spinning my legs faster? It just feels uncomfortable, and if I'm going slightly downhill at the time I'll start bouncing around in my saddle.