Yes, definitely turn off HT/SMT and use a single app thread per core with busy waiting. I'm working on a low latency application design guide exploring this more in depth.
I am not actually sure how precise this approach could be in theory, so if the noise floor could be low enough for it to matter, then it's certainly a factor for some applications.
If we prove that SMT has a certain bounded impact, then it may be possible to say that for a certain range of applications you get a 2x feasibility bump because you can leave SMT enabled.
People have a bad taste in their mouth that was left circa ~2000(?) from some Intel parts with a pipeline that was too deep. Ever since that was fixed most workloads do see a 2x speedup when enabling SMT.