Phil,
I'm hardly the expert around here but no one seems to be answering your question so I thought I'd jump in with my tuppence worth.
The head mech for the old Trump site here in Buffalo just pulled out of the driveway half an hour ago with my bike to do the 20k check up and other work. We got talking. He told me that the difference between the Mobile T-1 or whatever it is that Triumph demands we put in our bike and the "non-Triumph" Mobil equivalent, is the sticker on the bottle. It's marekting hype; same oil exactly. Anyhow, I've been using Valvoline 4-stroke oil for over two years now and I get better transition between gears than I did with the Mobile stuff and at $4.00 a quart too.
As is the case with a lot of the stuff I've done to my bike, Gary James is my reference. He says he went and did the research and it specs out as good or better than the recommended Mobil stuff. I tend to take people at their word if they throw it in their bike too and if there's an anal retentive guy out there that beats Gary for attention to these kinds of detail, I haven't met him yet. So anyhow, I use the Valvoline 4-stroke 10W-40 (I don't have a bottle sitting around but I think the Prod. # is VV 740) in the early season and to clear out the grunge from the bike sitting. Then after about a month of riding, I swap it out for the 20W-50. (Prod. # VV 743) Also, in both cases, I substitute half a quart of Lucas Oil Treatment for half a quart of the oil.
Hope this is useful.
BB
http://www.valvoline.com/pages/products/product_detail.asp?product=76
