I've been running Helix Ultra ECT C2/C3 0W30 (PP Euro LX) in my Saab turbo for 3 years (since I got it.) The lifter clatter on startup is gone, the fuel economy has improved and the oil consumption has fallen.
It's expensive, but with a VI of over 200 and HTHS >3.5 loads of Boron it's hard to top.
I've been using VW504 oil in my GLI for almost 4 years now with no issues. I've never noticed any oil loss between changes and do 5k mile oil change intervals.
EDIT: I do not have experience with either brands the OP mentioned; I have been using Motul 8100 X-Clean+ 5w30 since it meets VW504/507 and I like the price.
(Both of these oils are warranty approved for this application as each have the VW 504 certification).
I would use Castrol 0W40
BUT, if you are stuck on VW 504.00 use Mobil1 ESP 5W30.
Mobil1 ESP 5W30 is more stout oil than both you mentioned. Pour point is -45c, and regarding cold start you will be more then fine. HTHS is 3.58 which is almost equal to HTHS of Motul X-Clean 5W40.
That is if you want probably best VW 504.00/507.00 oil.
If you are stuck on 0W, get Castrol 0W40 or even better, Castrol 0W30 ACEA A3/B3 B4.