Roughly 80/20 read to write. On the instance's gp3 EBS volume (which is pretty slow), we've pushed ~700 write transactions per second without much problem.

For small oltp workloads the locking is not going to be a problem. But stuff that holds the write lock for some measurable fraction of a second even will gum things up real fast. Transactions that need it for many seconds? You'll quickly be dead in the water.