W115 OM616 1974 240D

Only had it a couple weeks. When I bought it the dipstick was halfway between the marks, and over the last couple weeks it went down a little below half (leaves little drips on the driveway, and smokes a bit when cold) so I figured, "Hey, might as well top her off..."

I added about half a quart and brought the dipstick almost up to the top mark. It now seems like she is smoking heavily when accelerating, regardless of temperature. She used to smoke a bit when cold and when pulling away from a stop, or downshifting, but not really that bad. But after the top-off she now leaves a pretty heavy cloud (grey?) every time I pull away, or floor it in 2nd.

Been reading the threads about smoke and overfill, and it seems like I must have filled her too much, and that maybe halfway on the dipstick is just about perfect... So I guess my real question is:

Should I immediately drain off a little oil, so as not to damage anything, or risk a runaway? Or should I just let the old gal do her thing and burn up whatever seems excessive. I ask with some urgency, as I was planning on making a 300 mile round trip this weekend, including some substantial climbs up into the mountains.

Bonus Question:

Do the top and bottom marks on the dipstick actually correspond to any numerical values, or is this something I'll just kind of get a feel for as I do oil changes?

Thanks!