High Tensile steel frames are bound to be very flexy, quite heavy, or both, regardless of toptube angle.

As pertains to road bikes, in my size, I find sloping toptubes unattractive and unable to provide a ride better than the finest horiz. top tube frames. I'd be reluctant to purchase even an OS tubed road frame. I've tried Cannondales and no way I'm riding a century on one. I don't find compact road bike frame design to offer enough advantage to the end user to compensate riding such an ugly frame. My old Univega Super Sport and current Pinarello are just about perfect frames and both are horiz top tube.

I'd imagine for larger frames there might be more of an advantage. If a builder uses thicker tubing on larger sizes, he could likely go one size larger using the lighter tubing for sloping toptube design than with horiz toptube design and still get the desired stiffness.

On the other hand, there's NO WAY I'd want to go back to horizontal top tubed CX or MTB frames, for reasons other than perceived stiffness, and my mongoose has a fair amount of seatpost showing yet is amazingly stiff in the pedals.