In other words, if you care about performance go with Intel? As for vendor lock-in, how is relying on AWS specific hw much better (see other comments below)?
If you care about performance to the extent of inlining hand-tuned assembly, you almost certainly care enough to do your own perf benchmarking on your own workloads.
Presumably, you aren't doing anything special in those ARM builds, so you can use an x86 build just as easily (or a non-Amazon ARM chip) depending on cost.