Interestingly, I have been using RL 5w-30 for 8,400 miles so far. I plan on doing the factory standard 15,525 mile OCI in my 2000 BMW 323i.
Redline has been a mixed experience for me.
First off, their 10w-40 car oil vaporized in my Kawasaki EX250 at the rate of about one quart per week. I was very surprised watching it burn off so fast. I now use Valvoline VR-1 20w50 year round (+5 F to +100 F ambient) and it is a terrific oil. It boasts very low friction for such a high grade and extremely low valve train wear rates. Start up is a breeze even at 5 degrees. Oil burn off is entirely negligible and immeasurable.
As for my car,
The trouble I have had with the 5w-30 is cold start hydraulic lifter clatter when below 60-70 F ambient. However, there was a bulletin posted years ago regarding this issue with some oils and it is deemed entirely harmless by BMW engineers themselves. It is simply annoying for a few seconds. I did not have this issue with Valvoline 15w-40 HDEO and Castrol GTX 5w-20, but that was in the summer. I am contemplating changing to 10w-30 grade next oil change rather than a 0w-40 because I need a very high HT/HS viscosity for my driving style and I am not sure what to use. I have no clue whether a change in low temperature viscosity will alleviate the symptoms I am having at start up. In general, lower viscosity oils also have a lower HT/HS viscosity.
It seems that their 5w-30 has a lower coefficient of friction than all of the other oils I used so I can glide further when I let off the gas.
Although just about every fan of using Redline products in their BMWs recommends MTL, I am going to switch up to MT-90 in my manual transmission because the MTL does not provide the smoothest shifting performance. I have experimented with MT-90 in my friend's manual BMW and I am pleased with the results. I may post more about this in a few months.