I've done both 270 and 30-06 and the 270 had about twice as many split necks during reforming than the 30-06. We're still talking pretty small numbers, maybe 1 in 30-40 for 30-06 and 1 in 15-20 for the 270. In total I have around 200 cases in 8x57 and less than a half dozen of those actually have 8x57 headstamps.
The set of Lee dies I have has the lube escape port (the hole that allows excess lube to get out of the die) on the bottom edge of the shoulder. This leaves a gouge on the shoulder of the case after the conversion that was a weak spot that caused cases to split at that spot after sometimes only 2 firings after the conversion. I bought a set of Hornady dies and they worked great. I've read many reports of RCBS dies also not having any problems. I've read at least one report of Lee dies not doing this so maybe the location of that port isn't too consistent. Regardless of brand check for marks, significant scratches, or gouges after the first couple pieces just in case.
You may need to neck turn the cases after converting to get them consistent. Most of my cases had steps in them once a bullet was seated from where the shoulder transitioned into the body/side wall of the original 30-06 case. They would chamber but some were very stiff to close the bolt and had scratches and marks on the thicker part of the neck below the step so I figured that's where they were sticking. I turned them all down to .011" neck wall thickness as that was the thickest that would clean up all necks completely and uniform them; YMMV. It was also the thickness on a lot of my factory 308 brass so I figured it would work fine (this was my first time neck turning cases). I bought a Sinclair case neck turning tool from Brownells for around $40 I believe. Now I use it for uniforming a lot of my brass and have picked up mandrels for .224, .264 (6.5mm), and .308 for uniforming/accurizing other cases.
I did some of my first cartridge conversions with RCBS case lube 2 in the dropper bottle but switched to Imperial (now Redding) sizing wax after reading some great comments about it online. I have now switched to Imperial/Redding sizing wax for all cartridge lubing applications and haven't touched RCBS or Lee case lubes in over a year. I bought mine from Henry at Budget Shooter Supply.
I experimented with annealing before converting, after converting, and both, and didn't notice any significant difference. What I found odd was whether I annealed before converting or not I got just as many split necks from the conversion process. It may have taken a little less force, I never did a side-by-side comparison at the same sitting, but it didn't help splits. I now only anneal once after the conversion process is finished.
The process I used was:
size in steps - turn the die in 2 full turns per stroke on each case
trim - I used a Lee trimmer in a drill but in retrospect it may have been easier to cut it down almost to size with a Dremel cutoff wheel and only do the final trimming with a normal case trimmer
neck turn - .011" neck wall thickness
FL size again
anneal
load
In total this cost me an extra set of dies ($50) and a neck turning tool ($40) and an 8mm mandrel (<$10). The neck turning tool I would have bought anyway so really it cost me about $60. Sure, it took time, maybe an hour for every 30-40 cases, but buying 200 cases was impossible at the time (peak of shortages when no one had any components in stock), would have cost more than twice as much, and I have probably 1000 once fired 30-06 cases and I don't own a 30-06 (yet). When I did it I had the time to spare so it made the most sense to do the conversions instead of buying brass. Others situations may be different.
