Well , because you have both "coolant in oil" AND "oil in coolant", it still could be the oil cooler.
I'd be kinda curious about how many times was the engine shut off, DURING your last 600 miles(giving coolant pressure time to drip into oil pan); OR maybe just before your 600 miles "weekend haul", the oil cooler actually was already letting coolant into your oil pan, right at your very last shutdown, before this last 600 mile weekend.

You asked about pulling oil filter and looking for drips of coolant, with radiator pressurized; if you want to do this, then I would also remove the two test port plugs(point downward, underneath) on the oil filter base, too. They tend to be 1/4" NPT, but are sometimes inside an adapter, that is an o-ring style. With all three removed(oil filter, and two test plugs[front and rear]) then that should unsure that coolant drips should be seen from the oil cooler area.
Although, this isn't how we would be troubleshooting, at the dealership.

We would get engine hot, then pull the oil pan, with pressure on the cooling system(for your style of complaint/failure), BUT I would also be looking at the water pump weep hole, and probably stick a wire in there and see IF I got a rush of coolant pouring out, once the wire penetrated any crude/build-up in that weep hole. IF plugged; then this would only explain the coolant in oil BUT NOT the oil in coolant.
{Edit: We may also just pull the oil cooler again, too, to test. I don't know how much oil you had in the radiator?}

1. You could have just an oil cooler problem(but for that much coolant in oil pan, I would actually suspect a lot of oil in radiator, too, I mean a lot!) But sometimes the leak area "flows" one direction much easier than the opposite way.

2. You could have both oil cooler and water pump problem

3. You could have lower, liner o-rings failing and pinholes in liner problems($$$) This can explain both conditions, too.

Head gasket failure, for your complaint, doesn't really add up.(pressurized oil goes to the head, thru a hollow dowel with o-rings around it=very solid, reliable area)= wouldn't explain "oil in coolant" part of your complaint

Note: the reason we get an engine "HOT" before pulling an oil pan, is because you only get this one chance for the engine to be warmed up, before you disable it; SO if you don't happen to find the culprit "HOT" then we just let the engine cooldown, overnight, and we can test it "COLD" the next day(still disabled); with and without pressure on the radiator. [ this kinda applies for those really hard to find problems= like an oil sample states some signs of coolant in oil, BUT no visual signs]
Yours shouldn't be that difficult.