I've done 2 chain and sprocket swaps using Triumph OEM stuff and Brent's sprockets with a DID chain, and haven't noticed any difference in how long they last. Even though your rear sprocket looks OK, I'd change that out too.
Realistically though there just aren't enough of our bikes out there with tons of miles on them to get a good idea of which chain and sprocket combinations last the longest. There's also other variables to consider like how often you clean your chain, how hard you launch your bike off the line, etc.
