I knew I could count on this group to have covered this already! Thanks everybody!
I always put Premium (~91 octane) in my (now sold) 2001 Sprint ST, as per the owner's manual. And out of habit, I put Premium in the Striple for the first few tanks. When I got around to reading the manual carefully, I was surprised to see 87 listed as minimum. I've been putting Plus (~89) in for the last few tanks and listening for knocks, and reminding myself to check here for the group's wisdom. The engine has been running fine. After this thread, I'll switch to Regular (~87) for at least 1 or 2 tanks, and listen again for knocks.
I'm surprised the higher compression Striple can take lower grade gas than the Sprint, but I suppose it's a more sophisticated engine management system.
As for detergents and other additives, I did a bit of Googling. I couldn't find anything on Chevron
website detailing exactly what they put in their fuels (other than "Techron" for Chevron and Nitrogen for Shell). I also found this interesting Wikipedia page
(so take with a big grain of salt) that says "Top Tier" detergent standards must apply to all grades of gas the retailer sells.
Based on my experience cleaning carbs on old bikes, and doing fuel filters and other fuel system maintenance on the Sprint, I think if the bike is ridden regularly (so the gas doesn't stale and leave deposits), and I'm putting standard US retail pump gas in your bike (nothing from a rusty jerry can in a developing country), and the engine doesn't knock, I'm happy putting the lowest recommended octane in the tank.
BTW, I had a 2002 Volvo V70 T5 that also "recommended" premium gas, but said lower grades could be used. It would run on mid grade ok, but I noticed occasional knocking on 87. With the high pressure turbo, the engine management system couldn't cope with lower octane.
Thanks again for all the great info!