At 3k and 6k I'll change oil filters(Ford FL-820S) and top off and at 9k I'll drain it all and fill with 6qts of Amsoil 5w-30 and new filter. My Cobra has over 16,000 miles.
I use amsoil 0w30 and change between 4000 and 5000 miles.I intended to change every 5000 + but after reading about all the silicone in the oil with K+N air filter, I backed off abit. I have had the oil analysed the last two times and it holds up very well at those intervals though silicone still looks high to me.I went 10000 miles in my civic with the same oil and the viscosity broke down so I don't believe amsoils or anyone else's claims for extreme intervals on full synthetic.I changed the civic at 6000 the last ime and oil was still good so will try for 7500 on next change and have it analysed again
I figure Ford thinks their pseudo-synthetic 5-20 can go 5k miles between changes, so 5k miles with Mobile 1 5-30 should be fine. I use the motorcraft filter as well.