I have a 'firm' Bridgestone set which I got after putting 15K on my originals. I have put 25K on my new set, the Bridgestones, and am very pleased at their life. I get them rotated and balanced every 5K. I recommend having that done at the tire dealer. I am expecting at least another 25K at the current wear rate. You can look for my prior posting a long time ago. Also, make sure your alignment is good. The dealer aligned my wheels incorrectly and I had to have it redone. This can cause bad tire wear!
I have heard alot about Lexus Dealerships messing up alignments your not the first person to mention this a couple of mechanics I have talked with have complaned about cars comign from Lexus dealerships (Park Place) being completely off.