It doesn't sound like you have a high crankcase pressure problem. But if you do have an air leak somewhere in the engine, I would imagine at high load the air rushing past the flame trap in the air intake hose can create enough vacuum to suck too much crankcase air if there is a leak on the other end. More air will cary more oil fumes and therefore increase consumption. Just a theory.
Most cars with PCV valve also have a crankcase air intake somewhere. Volvo's system relies on sealing off the crank case completely except for the flame trap hose.
I replaced the oil cap seal a couple of time but it never cured the oil that would leak out onto the plastic spark plug cover. Eventually I replaced the plastic oil cap with an old school early 240 all metal cap along with a fresh seal.
oil cap picture 1
oil cap picture 2
Originally I replaced it for looks but it turned out to be a higher quality piece. You can adjust how tight it is by bending the little metal ears on the bottom.
My engine consumes a little less than 1/2 a quart of Mobil 1 5w40 in 5000 miles. It just passed 111,111 miles today. A mile stone in my book.

EDIT: the "Hardcore Home Depot Racing" intake is 4" diameter, not 3" as previously mentioned. You also have to remove a couple of plastic covers behind and to the right of the headlight in order to remove the old intake. Its a tight fit.
Justin