Any optimized miner exists?
Not that I know of. If you compiled the miner yourself playing with compilation flags can help a little. If you have an AMD CPU you're probably limited by L1 cache, so I would suggest something like CFLAGS="-march=native -Ofast -msse4 -DSPH_CUBEHASH_NOCOPY -DSPH_SIMD_NOCOPY -DSPH_CUBEHASH_UNROLL=2". (Cubehash defaults to unroll 16, doesn't support none since even and odd laps are not the same.)