Personally, I wouldn't trust either one. M1 is supposedly fully synthetic, but they don't commit to anything on the label. I'd bet it uses mineral based stock since they won't say otherwise in writing. Castrol admits that Syntec is made from mineral stock, and they say that Edge actually uses POA, but they won't say how much... therefore, I still don't trust them. That said, both oils are probably good, but I would be careful of claims that you can go X number of miles between changes.
Personally, I use Amsoil 5w-40 European Car Formula. I will be changing every 7k-8k miles or so (not 15k - 25k as Amsoil propaganda would suggest - although may be possible if you drive LONG distances without shutting off the engine much and you change the filter at least once or twice in there). I haven't actually driven far enough to change it yet, but I've had no problems in about 2.5k miles. I've always used Amsoil in all my cars since about 1998.
NOTE: I do not use amsoil transmission fluid with my transmission... I've used it on other vehicles and loved it, but it has never been tested well enough with the ZF tranny, and I'm not about to take one for the team with something that critical.
If it makes any difference, BMW OEM oil for the M62 engine (02-05) is FUCHS Titan SuperSyn Longlife 5W-30. I pick this up for £16.50 per 5L from German and Swedish, or it's about 3 x that in the shops. I find it eliminates the Vanos rattle and stays clean until the next oil change (although I run LPG so oil stays cleaner for longer).