iPXE slow to download vmlinuz and initrd

[NiKiZe]

Check the link speed at the switch port when iPXE is booted.
but even with 10Mbit/s you should have around 1MiB/s which means your kernel should be loaded in under 10 sec.
It might be that interupts is not available on that machine, and that would explain the slow speed if iPXE have to poll the nic for each packet
Realtek have quite a few buggy chipsets, try to grab some other nic instead, such as an intel gigabit nic instead.

I would also be interested to know what the embedded nic is, and what speeds you got with that, one solution might be to still booting over the fast ethernet nic, and then disable that and only use the gigabit nic when Linux boots.

If you want to have kernel and initrd on disk instead, just use grub, copy over the cmdline, no need for iPXE