I believe in dino=3000, synth=6000 -- For the Connie. I am no expert, its only my opinion. I have never done oil analysis on the Connie. I have done some on the wifes old car, and have done many many samples on my truck comparing both Dino and Synth. Oil Analysis in the truck shows that Synth definately holds up better. Wear metals were about the same. I didnt see any difference there. From a viscosity and additive package viewpoint, the synth oil hold its viscotity longer, etc. Still I think it depends. I some ways I think the MFG's use 3000mi as what they list in the manual to be on the safe side of things and cover all worst case scenarios. -- Meaning for example I remember back when the wife and I had a 626 and a little dodge colt. I used Mobil 1 in both. In the 626 with the Wife driving at 5K the Mobil 1 look like you just changed it only a few weeks ago. At 10K it was finally looking like it needed changed. I could never bring myself to go more than 10K. But at 6K I would pull the dipstick and examine the oil and wonder why I was bothering. WHERE on the colt with my driving that thing was looking ready to change at 5K even with Mobil 1. 2500 on dino was looking black, dirty and felt thinner compared to new fresh from the bottle. The 626 at that interval was barely starting to brown. Still way too much golden color to the oil at 2500mi on Mobil 1. But then the truck for example, always gets firty fast no matter what. Its a diesel and soot gets in the oil. Here w/o a bypass filter setup I am not sure I would do extended intervals at all. Some do. But I wouldnt. Just too much crap getting into the oil. Sync also has better temperature characteristics. For turbo charged vehicles where oil can sit in a hot turbo after shutdown, I would tend to stick with synth. So I guess where I am going with this is that I believe the blind 3000mi no matter what rule was dreamed up my MFG's to cover the masses under worst case. Hell even many/all onwers manuals I see have something like 7500mi under normal conditions and 3750 under heavy duty conditions. Then of course they list what qualifies as HD. And just about everything does. But my point is even the MFGs of our vehicles make an attempt to recognize oil intervals vary under different conditions. I believe in analysis, and using your judgement to come up with what is right for your vehicle under the conditions you drive it in.