I'm also thinking about switching to full synthetic. Will I benefit from switching to synthetic at this mileage? I basically want to extend the recommended oil change intervals to something like 8k to 10k miles. I'm going 10k intervals in my A4 and it's as clean as new under the valve covers, so I'm comfortable with doing those kinds of intervals. I just don't know much about Lexus' and my A4 has always had full synthetic since it was new, it's now got 142k miles.
I don't want to turn this into a debate about oils (I've read some threads in the archives), I'm just trying to find out what weight oil is recommended and what you all are using.