Oh yes, in particular in Ultimates the serum has noted effects on the brain functions. 616 Steve is supposed to have increased multi-tasking abilities, aiding his tactical grasp of a situation, but Ult Steve has that aspect highlighted much more. Tony's twin does not get as much panel time as one might like - Millar left Marvel to write independent comics, and wrapped up that plot. They do have some delightful bickering, however.

That's fine! Are you on Dreamwidth at all, or just LJ? I do most of my reading on DW now.