Suffering from a head cold today, but decided to go for it anyway, and completed w4r3. Wouldn't say it was easy, but got through it OK, and had enough left in the tank to up the pace slightly for the last couple of minutes.
All good, and looking forward (I think) to the ramp-up next week, even if the thought of running 20 minutes non-stop sounds a tad ambitious. Still, Jo Whiley knows best