Impose a minimum write size for TLS writes
If our TokenBucketRefillInterval is very low, we'll frequently wind up with very small writes, which can be exceptionally bad with TLS. One answer is to say "don't do that then" and keep TokenBucketRefillInterfal to about 100msec or so. Another answer is to nagle our TLS writes, and never write less than the full amount in the output buffer, or one cell, whichever is smaller.
For non-TLS writes, the kernel should nagle for us, so we're probably fine, though it might be sensible to impose a write threshold there too.