280 transactions per second sounds about right for a system with spinning disks attached. A transaction is committed when the data hits the log and in general you can do this once per revolution of the disk platter. If there are simultaneous transactions they can commit together.
Anyone who gets thousands of transactions per second either has a battery backed cache on the hard disk controller, or does not have the D in ACID. Or is running on SSD disks.
The fact that disks and operating systems have silently been ignoring fsync requests has gotten people used to completely unrealistic numbers.