When I was in my Walmart, I asked the stock clerk why they didn't carry Mobil-1 20-50 VTwin MC oil. He said they did, but they kept it in the motorcycle section which was separate from the oil place. He took me there where there were helmets, inner tubes and sure enough, V-Twin oil. Cost was $8.62 qt. So make sure to ask them if you don't see it.

 

Magnesium is used as a detergent to help reduce and neutralize sludge and varnish deposits in the engine. V-Twin has more of this additive than 15W-50.
However, calcium is also used as a detergent and does the same things as magnesium, and 15W-50 has more of this than V-Twin. So both could be considered comparable for engine cleaning capability.

All oils are designed to do the same things- lubricate, reduce friction & wear, clean, suspend contaminants, etc. They all achieve this via the cocktail of additives mixed with their base oil. Usually if oil "A" is deficient in one additive as compared to oil "B," it will be countered with elevated levels of other additives to compensate and achieve the same result. This is why, given a maintenance regimen comparable to what the OEM specifies, you'd be hard-pressed to find one synthetic oil that will dramatically extend engine life over all the others- regardless of the oil manufacturer's marketing hype.

Here are the VOA's with Syn3 added. The Mobil VOA's were done in 2007, the Syn3 in 2005:

Silicon: M1 15W-50: 9ppm M1 V-Twin 20W-50:10ppm Syn3 20W-50: 5ppm
Boron: M1 15W-50: 228ppm M1 V-Twin 20W-50: 188ppm Syn3 20W-50: 271ppm
Sodium: M1 15W-50: 13ppm M1 V-Twin 20W-50: 3ppm Syn3 20W-50: 0ppm
Magnesium: M1 15W-50: 43ppm M1 V-Twin 20W-50: 538ppm Syn3 20W-50: 740
Calcium: M1 15W-50: 2464ppm M1 V-Twin 20W-50: 1899ppm Syn3 20W-50: 1342
Phosphorus: M1 15W-50: 1193ppm M1 V-Twin 20W-50: 1142ppm Syn3 20W-50: 997
Zinc: M1 15W-50: 1315ppm M1 V-Twin 20W-50: 1352ppm Syn3 20W-50: 1068
Molybdenum: M1 15W-50: 90ppm M1 V-Twin 20W-50: 0ppm Syn3 20W-50: 1ppm

 

I justwent towal-mart for 15-50 and some 75-90 gear oil. They had the 15-50 for 6.97 a quart but did not have the gear oil so I figured I would just go to Advance auto and get everything and only stand in one line. I get to Advance and much to my surprise they have Mobil 1 V-twin but only had 3 qts. The kid at the counter said they have only had it for a few months. They are going to have the other qt. at the store in 4 hours for me. The surprise to me was the v-twin was only 2 bucks more than 15-50 so I will try it. Also they have filter wrenches for 4.94.