Butryflynet, great idea with the few day rental, probably via Craigslist..
On the hours from SF to the Oregon border, I only know highway 101 very well, and not highway I-5.
In good traffic right out of SF (varies with time of day, biggest clog is going by the city of Santa Rosa), it used to take me 4 1/2 hours max, including gas, shortish food stop (say, in Healdsburg to get a sandwich-to-go at the Oakville Grocery - don't get me going on that wonderful place) to get to the coastal cities around Arcata, which is about 75 miles from the Oregon border. So, let's say six to seven if two stops, to the Oregon border. More time, of course, if you're coming out of SF at rush hour. (I didn't do the miles of old redwood forest at high speed even though traffic was always light, too much beauty to rush.) But then FD won't be doing 101. I-5 may be twistier longer, don't know.
(reminds me, I have a thread called "Driving 101". I'll be back with a link, as it isn't so much about 101, although it is about it, as it is about the sensibility of driving.)
But that reminds me, FD, bring an I Pod or CDs, whatever, as radio reception can go blanko for a long time in forest areas, or at least did a couple of years ago.