Slow speed of AMT Redirection may be result of starting AMT redirection from S5 state where AMT limits LAN speed to 100 MBps only and does not renegotiate it on power on.
Try turning it on first, then as soon as power state transition happens start IDE-Redirection with Reboot to IDE-R CD image -whithout sutting it.
if your network is 1Gig AMT will keep this link speed.
IDE-R have native speed limitation over Wired LAN at approx 2000kbytes/s - due to ... Intel ME ucontroller beeing small best IT friend inside chipset.
please check Faster Booting Over IDER https://downloadcenter.intel.com/download/20960/Intel-vPro-Use-Case-Reference-Design-Faster-Booting-Over-IDER reference design.
Boot stopping may be matter of ... Secure Boot being enabled (try disabling it for OS reimage time) and/or UEFI/Legacy BIOS Boot settings - try the other boot option.
IDE-R Intel HD CD/DVD emulated is a standard CD/DVD device with ... Intel VID/PID - some preboot images of bootable ISO (the one that emulates FDD from CD) do not recognize it as standard CD/DVD and the main part of OS image storage is not visible.
You may need to modify your OS installation boot image to include standard CD/DVD driver for those Intel VID/PID device.
Above link may be also helpfull for this.
Intel EMEA Biz Client Solution Architect