Q,
Here's what I learned when trying to improve on "one design" club pylon racers.
Frequently the intersection of the fuse and stab (stab and stab in your case) creates more drag than the surface it self. With the double "T" stab you would be roughly doubling the drag vs. a single T-tail. In addition you would see drag from the pressures between the two stabs and a loss of efficiency from the lower aspect ratios.
The benefit of a T tail (besides keeping the horizontal out of the weeds) is that it only has 2 plane intersections vs. 4 on a conventional tail. The greater the angle (>90 deg.) between the surfaces the less drag those intersections induce. This is also why 110-120 deg. V tails are so popular.

Chris