For the record, I commited nerdralph's improvement: https://github.com/mbevand/silentarmy/commit/a33a9065528599f5821c4ca02c5f63fa167e9afd
See also https://bitcointalk.org/index.php?topic=1671021.msg16788712#msg16788712
It appears to neither improve no degrade performance on an R9 Nano. But some people report an improvement. And "sa-solver --nonces 100" reports a 15% degradation. So it's really inconclusive...