That's a sweet deal for the Dusk.
I just got the 7hz, was actually surprised how fast it shipped. It's a good set especially if you don't already have a set of planar in your collection. However, I don't think it blows away the P1. They are about on par with each other from what I can tell. The 7hz is much easier to drive though. So if you already have the P1 I'd say skip it. I'd you don't have any planars, the 7hz is a solid first set.
Edit: 7hz Timeless is highly dependent on tip rolling. Stock fitted tips are ok but kinda lean sounding. Just tried cp100 on them and they really brought out the warmth and textured bass. Much better. Audeze LCD-2 like versus the P1 which sounds more similar to HiFiMan. Awesome planar sound out of the BTR5
Sundara's still trounce all over both of them though. But for a portable planar setup, this is as good as it gets.