Road Cycling - Sloped top tube

Does anybody have a road bike with the top tube slanted down like a mountain bikes? All of Schwinn's road bikes are built this way, and several other companies have bikes with the top tube slanting down.
It seems to me that with a slanted top tube the bike would put you in a more upright position, which is less efficient. But maybe I'm wrong.What is everbody elses take on the slanted top tube design??

The sloping tube has no effect whatsoever on the riding position. You just take the top tube from the horizontal position and shift it down at the back. The seat angle and effective top-tube length remain identical.
It results in a frame which is lighter and stiffer, with more crotch clearance, but retaining a useful amount of head tube .

Is it better to have a long head tube?

Headset bearings work better when there is a longer headtube. Small 700c bikes are notorious for eating headsets.

Time triallists need a really low handlebar to get aerodynamic , so may benefit from a short head-tube, but these machines dont have such a hard life. For longer stage racing and daily training you need a more comfortable position, so the bars are usually only 1-3" below the saddle.

Some Lightspeed frames are built with a headtube extending an inch above the top tube. These are serious racing machines, and their design consultant is Eddie Mercx.

Can you mix drivetrain components on a road bike like you can a MTB?

with a little care and expertise.
Friction levers will shift any mech/gear combination.
Campy will shift any front mech/gear system.
At the rear the shifting precision is too tight to mix, but you can get cassettes to match any hub/gear system.
eg Shimano hub, Marchisio cassette, Campy mech and levers.

There is problem with chain compatability with 9/10 speed systems.

Its a problem for touring bike users, since no-one makes a proper touring groupset to use with dropped bars.

Ok.
The bike I'm looking at is a Giant OCR 3. It has a Shimano Sora drivetrain on it. The problems with Sora is that you can only shift from the hoods, not the drops. But to get Tiagra you have to go up to the 800-900 dollar range, I am not in that price range. Can I switch the brake/shifters of the Sora to brake/shifters of Tiagra or 105?