I just went through this with my TV. From what I've read, you want to use the lowest backlight setting you can, while still attaining between 30-ft ftL at 100% white. You also want the highest contrast setting that doesn't clip whites or colors, and watch out for discoloration as you turn up the contrast.
In a dim room, I've found that I like about 30 ftL. I was able to achieve this with contrast at 98 and backlight at 4. My only problem is that at that contrast setting, I begin to run out of red, but it doesn't happen until over 235 (up in the above white range). If I look at the white level pattern with the flashing bars in AVSHD, some of the higher bars look pinkish. I've been told this is really an optical illusion because the background on this pattern is actually above white (255). So my eyes "see" the above white as white, even though it's too blue, and the other bars look pinkish. I guess ideally, you don't want any
discoloration, but I'm not too concerned since it's above 235. If I lower contrast, I'd have to raise the backlight, which would hurt black levels. If there's one thing I've learned, it's that a lot of time, you have to compromise.
Anyway, it sounds like your methodology is correct.