Reading the thread on dolphin technique brings to mind some work I did on
MacCready. If you do the sums in an 'ideal' flight with one climb and one
glide in flat air you find two things:

1) You can be well of the ideal MacCready speed (10%) before it makes much
difference in XC speed, and

2) that there is a smaller price to pay for flying too fast than there is
for too slow.

This you can see in the polar curve. The curve falls off quite gently
compared to the tangent line at all speeds and even at best glide you might
as well fly a few knots faster. Especially in a flapped glider.

Picking up on Steve's comments I whole heartedly agree that you don't want
to fly too fast and let the ground get in the way. It is also true that
flying to slow lets you find better thermals.

So, my rule of thumb is simple. Fly too fast at height and too slow when
low or twitchy.