Are you sure its optimized? I cant compare the gpu performance but when it comes to cpu, poclbm-skc hashes around 50% slower than skeincoin-cpuminer on the same cpu. I dont have much time right now, but I can compare it tomorrow.
Maybe we can create some kind of a benchmark to see the performance of particular gpus?
In my case its:
7950 - 180MH/s
r9 280x 200MH/s
Overclocking can get you another 5-10MH/s
5870 at stock core (850MHz) - 95MH/s
7870 (Tahiti) at 880MHz - 94MH/s
6950 at 900MHz - 103MH/s
6930 at 860MHz - 93MHz
Basically all cards giving around 90-105 MHz on my setup, overclocking doesn't change it a lot. On scrypt 5870,7870,6930 have performance close to 400KHz, and 6950 runs at about 450KHz, so current Skein-SHA2 implementation has 230-280 times higher hashrate than scrypt.