The 1st one will only go 1000-2000 miles...it's going to filter out all the crap that's been floating around your motor for years. After that, 4000-5000 miles depending on the quality of the oil. Each motor is different...the filter element in a Trasko is essentially a small roll of TP. When you pull it, you will be able to see how dirty it is and adjust the next change accordingly. Change the Wix every 4000 miles. BTW - the oil is still going to darken over time (not as bad though)...that's what all oil does when exposed to the heat in an engine.
Assuming everything else (wear metals, presence of coolant, fuel dilution, etc) is ok, base your oil change on TBN. That is the ability of the oil to neutralize acids...when it drops to less than 2, change it. Blackstone is good...every 4000 miles is sufficient (you can time it with the Wix change):
http://www.blackstone-labs.com/
This little gizmo make taking a sample easy:
http://www.supramania.com/forums/showthread.php?t=38929
Just drain a small amount into a pan, then catch your sample in the bottle Blackstone provides. Be careful about touching the inside or any contamination at all, the analysis is very sensitive. With the Wix filter change and the amount you discard as part of the sampling process, you add oil back to full (one quart over the dipstick mark on the 7M). This helps replenish the additives...use the same make/viscosity oil.