Oh dear - I just attempted W6R3 without success - managed about 14 minutes before I got a stitch, slowed down a little and my motivation just slid away from me. I just hate the disappointment afterwards. As lots of people have said W6 is deceptively tricky, but I really didnt have any problems with run 1 or 2 this week. But I'm struggling to keep going with the longer runs, and I think it is rather to do with motivation. I've done all my runs except a couple in the gym on a treadmill, and I do tend to 'clock watch' a little. I did do my W5R3 outside and found that the time seemed to go a little quicker, so don't know if this might help (however running outside where I live generally involves a big hill, which seems a little daunting at the moment). I've also tried the breaking it down into smaller 5 minute runs thing which sometimes helps too.
So I guess I need a little inspiration - what keeps you going when your gremlin is just telling you to stop?