Thanks guys, I'll go with the shorter probe since I don't want any meat to interfere with the probe. In the vast majority of cooks I don't think the 4" would be a problem, but there could be a problem on others. I just didn't know if the difference between lid and grate temps was enough to matter.
I may go with the weber 70180 since it should be a better fit than the Tel-Tru. I'll test it for accuracy.
Right now I use a 12" turkey thermometer that has a clip. I can adjust the length but it's top heavy and not real stable. I'm always afraid it might fall out when I remove the lid. Should have gotten a shorter one. Regardless, I can't adjust the top vent with it in.
Thanks again.