I won't bother burying the lead here, it's all about zip-ties. I've only had my Ultimaker for 3 weeks, but it seems to have solved the only issue I had after my build.
Like others, I have a lot of issues with the horseshoe clip just not putting enough pressure on the clamp. Owen's Hot End mod worked for a while, but I just couldn't keep it tight enough. Part of the problem is that the bowden tube was pretty eaten up from the teeth on the clamp...at one point I even cut a clean edge on the feed side of the tube and flipped it around. This held for around 3 hours of printing before another plug formed, and well, you know the story. At least I can take apart the hot-end like a pro now!
So I've ditched the clip completely, and just cinch a zip-tie around the clamp, really letting those teeth dig in. You'll also notice in the photo that I've added another clamp on the top of the hot-end, which seems to help distribute the pressure put on the tube, both during extrusion and gantry movement.
I can't say it's pretty, but I've gone through nearly 100m of filament since, and can get functional prints (parts, non-visible pieces, etc) running reliably at 150mm/s. My hope is that this cheap and easy fix is of help to someone else out there. If it is, let us know!