Disabling hyper-threading is highly unlikely to produce a 30% performance hit. Most highly optimized software disables or avoids hyper-threading because doing so increases performance.
Hyper-threading tends to benefit the performance of applications that have not been optimized, and therefore presumably are also not particularly performance sensitive in any case.
In highly-parallel workloads like rendering (ray tracing) where pipeline stalls due to loads happen quite regularly, it's fairly easy to get 20-35% speedups with HT.
Hyper-threading tends to benefit the performance of applications that have not been optimized, and therefore presumably are also not particularly performance sensitive in any case.