Okay, I wasn't going to get involved here but my god you have it all wrong people!
First off, when you say "feather" the throttle, I assume you mean light on throttle, and on my KM110r, I can make it so it just engages the clutch, and have no problem trimming WITHOUT full throttle. Maybe you run the standard round crap, but I use a triangle shaped line and it cuts great. Most of the work I do is not even at half throttle unless I am doing thick brush.
Second of all, the 4Mix is simply a vapor lubed 4 stroke, and you mention finding other ones without oil in the crankcase? I direct you to one of my old hobbies, RC cars. Planes have 4 stroke engines, and they DO NOT use oil in the crank case at all. Like Roger said, 4 stroke and 2 stroke refer ONLY to how many strokes of the piston, not oil systems or anything else.
Thirdly, I grease my head every so often. I check it when I have some extra time and remember, and if it needs some, I add a little grease. I ended up replacing my FS90r with a KM110r for the attachments, but my 1 year old FS90r still runs great but it is a little hard starting at times, but I think it might just need a new plug or a quick valve adjustment.
And lastly, I wouldn't run anything but Stihl either. I love the sheer power of my KM110r (even though it is the middle model, and a KM130r is better), and I love that the fuel tank lasts me around an hour of full throttle use. I love that I have the benefits of a 4 stroke like the high torque, better sound (subjective but I love the sound of my trimmers), and I never need to worry about changing the oil!