I have the same exact issue except I know where my coolant is going. It is leaking out of the t-stat housing.
If the head gasket was at fault, it would not really matter if it was cold or warm, it would run like shit, and it would smoke.
Not to mention, I could of swore op said the oil was clean.
I think the key is figuring out what all really changes that much from the outside temperature being about 40 or above, or below to cause these issues.
But honestly, to the op, get your oil changed if you haven't already and make sure it doesn't look like chocolate milk.
Most cars I have seen give off a puff or two of white smoke on cold damp mornings when started.
And back to the head gasket, usually when they blow to where the coolant leaks into the oil, it won't go away when the car is warmed up it will constantly smoke heavy white smoke. If the gasket blows between cylinders, it will really run like shit. It wont really have the problems you are having now, it will just have no guts what so ever. I have experienced the gasket blowing between cyliners in an 87 dodge minivan 2.2 and it ran ok at idle, but when you put a load on it it had no power barely could move itself. In an 87 mazda b2200 with a 2.0 i think it was, it blew to where the coolant mixed in the oil, that will smoke out a city block at least mine did but the truck actually ran somewhat ok. either case it sucks to have to change it.
Things that I am going to check on mine next as I have the same exact issues as you (minus the smoke and too much oil) is fuel pressure, o2 sensor and if that doesn't turn up the problem then I will try going after the egr.
Keep posting on what you find out hopefully we can get to the bottom of this without either one of us having to dump a shit load of money into them.