Ok. Thanks very much for the info guys. I'll get that trimmer in place and adjust for 10V at the drain. I guess I was too focused on the source voltage.
One issue for me is I don't own a scope. It would make things much easier if I did, but I may be able to wrangle something up using my DAW and some DC blocking caps. I have been meaning to get a simple tone generator.
Re-read the link MatthisD posted. Makes more sense on the second time around. So I'll set a trimmer for 10V at the drain, and then recheck once I have the mic constructed for drift, as well as listening for noise, distortion and such. Not going to be scientific, but should be fun!
Edit: Wow! Holy finicky batman! I started off with a trimmer, but after awhile, it was becoming troublesome, so I just made source R 10K, and measured drain voltages for each FET. Now they are all over the place ranging from 4V to 18V. Then I grabbed one of the 18V FET's, and got the drain to 10.22V using a 6.8K source resistor. So it seems that source R must be within a certain range to even get the FET to work at all, which explains every FET in my bag measuring the same at 3.9K. I also discovered that decreasing source R causes the drain to drop off sharply, which means the range is very small for adjustment. Now I understand why you have such an issue finding FET's that bias with a source R of 3.9k Gus. Very interesting.
I am going to go through the rest that showed a voltage over 10V @10k to see how many I can get to bias to 10V drain. Then I'll save all my pairings for the future.