Some of the 80bit algos are slow and unstable. SIMD can be 100% faster with a rewrite, but the 80bit is only used once in the 16 algo chain, so you only get around 1/16 +6.25% gain compared to all of the opensource miners. To optimize more you need to repeat the rewrite on all the algos in the chain. My mod is around 20-30% faster than the fastest opensource / enemy miner(24 hour test on the pool)
I have changed and optimized all of the 32 algos in the chain.