After first contact with Q, USS Enterprise-D did escape the cage of Q with Warp 9+. The cage started the pursue course to catch Enterprise. And, it overtook Enterprise's speed quickly. It was on Warp 9.9 when Enterprise stuck at Warp 9.8. Great... afterall, it belonged to Q.
But, the problem is: Why did the cage need to move with finite Warp speed? Or, why did it even need to pursue? Q was able to transport Enterprise from one part of Galaxy to another within a moment.