T tails are probably the most efficient type of tail, but they're only slightly more efficient than a more conventional design or V tail. There's also frequently a tendency to base rc designs on other similar designs that have worked in the past. There is no such thing as an optimal design since every design has tradeoffs. If you're trying to get every bit of performance you can out of a plane, a T tail or flying wing design is probably the best option. That said, you do not need a T tail to achieve high performance and if you look at full-scale high-performance racers, very few of them have one. It is completely possible to build a working one but there is absolutely not a requirement to for the performance you have described. Basically, if you want a T tail, go for it - I like the way they look and have included one on a couple designs - but they are harder to build and may not give you much benefit.
