I park near Woodingdean and it's about the same for me depending on the queue of traffic on Falmer Road - 10 (after final whistle, obviously) mins to exit ground, 35 minute walk, 30 minute drive (ish)
Agree - more like 40-45 mins (with no traffic) especially as roadworks on M23 before Gatwick slowing things down a bit. Best option though - I probably wouldn't risk the trains if I had a plane to catch