@dwillen: Yeah, a strong tandem team is a scary/awesome thing. When I ride with the DC Randonneurs, Chuck and Crista are always putting the hurt on the field with their custom-built Ti tandem. I've seen 'em pull a half-dozen strong riders for hours on end over terrain like ours...
@Brad: I think you meant "not allow", rather than "now allow". 'Bent zealots the world over have veins throbbing in their foreheads over that issue.
Speed bents: depends on what you're looking for, I suppose.
Want to set records? Go fully-enclosed streamliner: 80+ mph sprints on the flat with no assistance, or 53+ miles in an hour (note that Fast Freddy is a former Olympian, so that may have helped a bit...), or 25+ mph for 24 hours straight...
If ya want something that looks fast, the various carbon-fibre Batman bikes fit the bill:
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