I'm using an rfx6500 with a tsu7500 and I get instantaneous response on all my equipment. I control two DirecTv HR20s (and before that, an HR10) along with a DVD player, DVD recorder and CD changer.
All button pushes are sent/received immediately and are as effective as the original remotes. I do use the emitters for my a/v equipment and have the blaster on the top of the a/v cabinet pointed at the tv, which is on an adjacent wall from my a/v cabinet.
I would highly recommend the 6500.