Thanks for the reply Sebastian and sorry for the super long delay.
I am observing this behavior when using “ipxe.pxe” – I have not used any other one binary (not since I switched it to a production server a couple months ago).
Also, to clarify, the transfer rate is good once the transfer begins, it is only when it is “configuring net0” that it seems to be a slow link. However, I assume it is some hardware dependent issue as I just tried a random computer model and saw it was configuring at the expected 1Gb link speed.
So I guess the tl;dr is that this isn’t really a problem.