If I'm following you correctly, the car runs well a few minutes after starting? Can we assume you pulled the glow plugs in order to release the compression while rotating the cam? Seems like it would have to be a glow plug issue. Take all 5 out. Bench test them. Replace the defective ones. Don't over tighten the nuts that hold the wires on the GP's. See if this solves your cold start problem.

As for the expected increased performance, unless the valves were considerably out of adjustment a huge performance increase should not be expected.

Good Luck!