SS8_Gohan, if you are getting the M1 0W40 at $11/L I'd like to know where. TMost of the time the 0W40 is around about $80/jug or about $16/L so its not really much cheaper than the 300V. The cheaper M1 5W50 is around $11/L. Yes I would consider 300V a superior oil because it has a more stout additive package and a superior base oil. This is not to say the M1 0W40 is not a good oil - its probably the best M1 grade out and would have no qualms using it in most cars. If you can source the 300V in the 5W30 viscosity range, I'd pick that over the 10W40 providing your car doesn't use much oil and is not modified off its head. In terms of RP, I would choose RP over M1 if its the racing XPR oil range. Their ordinary street oils are still quite good but haven't shown stellar results in oil analysis. IMO, I'd pick 300V over Redline as well.
JonesyGTR,
1) The Castrol 0W40 is their best EDGE product. However considering its the same price as Mobil 1, I'd be picking M1 0W40 as it has superior OEM certifications. Then again my pick would be 300V over both of these, if you wish to spend that lil bit extra.
2) Diff oils, Redline is good stuff. I use their Gear oil 75W90 in the diffs. Doesn't matter if its LSD or not. Make sure is not the "NS" variant though.
3) Redline is definitely superior over VMX80. I'd be picking Redline MT90 for the gearbox, or Castrol Syntrans if that is available.
Hope that helps, although this advice is based on my experience only.