For my Gen I, I used a CeeBailey +4,+4 for 5 winters - good shield, EXCELLENT lack of distortion. Then tried a CalSci touring (too short, but smoother air flow than the CB), then a Rifle touring (with and w/o tuning block) - less wind protection, more buffeting, and more distortion than the CB, and finally a Rifle Jumbo with 1/8" - 3/16" spacers - looks like a barn door on the bike, but I'm now sitting in a perfectly still pocket of air with just a little bit of back pressure. Ah, search over.
In the summer, I run the stock shield with a Rifle tuning block for almost perfectly smooth air flow (at heights from between mid-belly to chin).
For comparison, I'm 6'0", but long-waisted (31" inseam), also have HELI bars that make me sit more upright.
Since people in the market for shields will be reading this thread: Anybody interested in a GenI CB +4,+4 and a (spare) Rifle tuning block? CB shield and the tuning block do NOT work together.