I ride a lot of long hills, and I use a front and rear brake. On long hills, once my cadence gets so high that I can't maintain smooth, continuous pessure on the pedals, I'm not able to control my speed without a brake. In that situation, the front brake makes the bike more unstable, but the rear brake brings it back under control instantly. I actually use the rear brake on the fixie more than the one on the road bike.
No matter how you brake the rear wheel- back pressure, skidding or a caliper- no rear brake will stop as well as any front brake. That is just a result of the laws of physics, and there is no exemption from those laws.
EM