Oil change frequency for highway mileage?

Hello. I own a 2003 Accord 4-cyl and wondering what, if any
difference, having mostly highway mileage on my car does to the
frequency needed for my oil change? The manual recommends every 5,000
miles/6 months. Does the fact that at least 75% of my mileage comes
from non-stop interstate highway travel at speeds of 70 mph help or
hurt me in terms of oil change frequency? Of course, with the long
commute every day, I get to 5,000 miles before 6 months, and thus not
only do I spend a ton in gas, but it seems I have to get my oil changed
every 4 months or so, which costs more money. Any thoughts and input
are appreciated. Thanks in advance.