We have 5 Competition clutch kits (4 stage 4s, and 1 ironman) in use right now. However, there is no feedback yet.
Competition stage 4 is equivalent to spec stage 3 but with a slightly stronger pressure plate.
From a driver standpoint, the Competition "feels" better. It lets you slip more/easier and is great for the daily driver setup. Their focus is more towards the daily driver. Once you start making a bunch of power, they get nervous.
SPEC on other hand, has great customer service, at a slightly higher cost. They go racing, and are a much larger company. So, if you want something equivalent at a lower cost, go Competition. If you want customer service if/when you need it, go SPEC.
I went competition for my 1jz because it was cheaper, the materials were the same as spec, and I'm a poor bastard.