I'm sorry I can't help you with the duplicates, but...
What sort of machine is your core running on?
I have a PIV 1.7GHz (single core) 1GB RAM Base 100T ethernet and network booting a machine the first time takes ages (I haven't actually timed it, but up to three hours atleast).
What you are in effect doing is installing LMCE on the machine using the core as a HDD (simplified explenation) and you know how long it took to install LMCE on the Core, and all the read/write to HDD is done over the LAN, so yes it can get "crowded" while installing.
What I do is start a PXE boot before I go to bed or work, when I get back the AV-wizard is waiting for me, I select the options I want and go eat dinner/breakfast. I keep the sound on so that I hear Sarah when she asks if I can "See and hear" her, then plug in the options for this MD and let the MD render screens for all my MDS (unless I plan to add more MDs) this also takes time.
The next time you boot however it's still slower than a local boot (everything goes trough the LAN, so GB LAN is probably faster), but not more than a minute (in my experience).
I have PXE booted, IBMs, Dells, HPs and only hit trouble with the Nvidia driver on an Asus laptop (except for the time)
So 30 minutes isn't near enough time. And yes, it does appear to stall at the running diskless.sh and other points in the process, but there's a reason your LAN is packed (to put it that way)