I ultimately went with the T12HT's myself, but I have no doubt that I would be very satisfied with the T8HT's. The fact is that both the 12's and the 8's require a capable sub.
In most circumstances in most residences, I think the biggest difference you will notice between the two is setting your crossover to 80Hz instead of 60Hz.
If anyone is curious as to whether the T8HT is up to the task, watch this Growler Duo youtube video
. The single T8HT is handling everything above 80Hz.
An LCR setup with the T8HT's ought to get it done, in your living room/theater, or a football field.