Advice please: Bike oils, Car oils?

[TimeOut]

I found this interesting http://en.wikipedia.org/wiki/Motor_oil , espcially the comment "All the current gasoline categories (including the obsolete SH), have placed limitations on the phosphorus content for certain SAE viscosity grades (the xW-20, xW-30) due to the chemical poisoning that phosphorus has on catalytic converters. Phosphorus is a key anti-wear component in motor oil and is usually found in motor oil in the form of Zinc dithiophosphate. Each new API category has placed successively lower phosphorus and zinc limits, and thus has created a controversial issue obsolescing oils needed for older engines, especially engines with sliding (flat/cleave) tappets. API, and ILSAC, which represents most of the worlds major automobile/engine manufactures, states API SM/ILSAC GF-4 is fully backwards compatible, and it is noted that one of the engine tests required for API SM, the Sequence IVA, is a sliding tappet design to test specifically for cam wear protection. However, not everyone is in agreement with backwards compatibility, and in addition, there are special situations, such as "performance" engines or fully race built engines, where the engine protection requirements are above and beyond API/ILSAC requirements. Because of this, there are specialty oils out in the market place with higher than API allowed phosphorus levels. Most engines built before 1985 have the flat/cleave bearing style systems of construction, which is sensitive to reducing zinc and phosphorus. Example; in API SG rated oils, this was at the 1200-1300 ppm level for zincs and phosphorus, where the current SM is under 600 ppm. This reduction in anti-wear chemicals in oil has caused premature failures of camshafts and other high pressure bearings in many older automobiles and has been blamed for pre-mature failure of the oil pump drive/cam position sensor gear that is meshed with camshaft gear in some modern engines."

The JASO T904-2006 also made for interesting reading being a set of tests for wet clutch compatability, http://www.jalos.or.jp/onfile/pdf/4T_EV0604.pdf but it is an addittional test on a good quality car motor oil and not a specific motorcycle oil. This also made interesting reading http://en.wikipedia.org/wiki/Motorcycle_oil.

I'm pretty sure moyorcycle oils are allowed higher znic levels to give better wear protection

[aum108]

So far, the 10W40 semi-synth oil is sitting nice in the XV250.
No more clutch drag whatsoever. When it's cold with engine off, and I hold the clutch in, there's no extra resistance with pushing the bike. Performance feels way better.

But...
When the bike is idling, or cruising along in low speed, the engine has a somewhat more metallic clattering sound. Is this a danger sound for the engine?