In order to provide the lowest access latency, the optimal place for the system swap file is on:

An external USB 1.1 4200RPM drive is an extremely slow storage option with high latency, making it completely unsuitable for optimal swap file performance.

A swap file, also known as a paging file, serves as an extension of physical RAM, temporarily storing data not actively in use. Placing it on the fastest storage device available, such as an NVMe SSD, minimizes the read and write times for these operations, significantly reducing access latency and improving overall system responsiveness, especially under heavy memory load.

While a 10K RPM SCSI drive is faster than some older drives, it is generally outperformed by modern SSDs or NVMe drives, which fall under the 'fastest storage device' category.

Placing the swap file on the operating system partition can lead to I/O contention between the OS, applications, and the swap file, potentially degrading performance rather than optimizing it.