Maybe it's time for me to step in an explain the difference between an T speed rated tire and a H speed rated tire.
For those who don't know, a speed rated tire means the tire passes a test where the tire, mounted against a test wheel in a lab, is held at the rated speed for 10 minutes. For a T speed rating, it's 118 mph, and for an H rated tire, it's 130 mph.
To do that the belt package of the H rated tire needs something to constrain the belt package from centrifugal forces - and usually that is a nylon cap ply,- across the entire belt width under the tread. There's some variations - sometimes an H rated tire will only use cap strips over the edges of the belts, and sometimes T rated tires will use full cap plies - but most of the time the difference is that cap ply.
Changes in tread rubber compound, changes in sidewall stiffness, etc. are NOT required to get the H speed rating.
There are 2 other things that need to be known to understand how this all works:
1) There is a technological triangle involving treadwear, grip (especially wet grip), and rolling resistance. To get better properties in one area, one or both of the other areas have to be sacrificed. (There are exceptions)
Since the additional heat generated by long wearing tread rubber is less significant that the effect the cap ply(s) has on speed rating, for practical purposes, a tire manufacturer COULD use the same tread compound regardless of the speed rating - Yes, even up to Y !!
HOWEVER, that is usually not what happens. Most tire brands consider the vehicles the tires are going on an make appropriate changes to suit the vehicle and create models tuned to a particular type of vehicle.
2) To get a better ride, (generally) the height of the filler is decreased. The filler is a stiff bit of rubber in the lower sidewall, mounted just above the bead wire bundle. Using a smaller filler also result is a less crisp response to steering input. Needless to say, people who drive high performance cars want that crisp response. Again, the models of a particular brand are tuned to the vehicle type.
But there can be quite a bit of variation from brand to brand in how they approach how they design there tires. So if one replaces an H rated tire of one brand with a T rated tire of another brand, one can't be sure if the differences experienced are the result of anything more than how the brands design their tires.
While the general trend is for higher speed rated tires to have tread compounds that grip better, but wear faster, and for higher speed rated tires for have stiffer, more responsive, but poorer riding sidewalls., when one is looking at replacing tires BUT NOT CHANGING SIZE, the difference in speed ratings doesn't mean much unless there is some other indication - such as a change in the UTQG rating.