The past 2 years I stayed at OKW for the marathon weekend. I believe the bus for the races only picks up at the front of the resort, so if your room is far from the front/main desk area you will have a long walk or you can take the internal bus shuttle. The bus wait times weren't that long last year and the traffic was fine getting to and from the start.
2 years ago the traffic in the mornings was ridiculous, and even though you can see the starting corrals from the exit it still took us probably 45-60 minutes to get to EPCOT. I don't know if we left later in 2014 versus 2015 and more roads were closed by the time we left.
I like OKW because the rooms are spacious, and they feel larger than other DVC properties.
What resort are you looking at renting points for, what size unit, and what days? I'm a DVC member and just checked availability for a few days around marathon weekend, some resorts have partial availability and others still have all dates open.