One of the main factors to consider when diagnosing leaf symptoms is location on the plant. A basic understanding of the difference between mobile and immobie nutrients is key to narrowing down problems that have similar symptoms. You are correct that a P deficiency will start low on the plant, so will N, K and Mg. Ca and Fe are the main immobie nutes that appear first at the top of the plant.
So back to your question...the issue is clearly at the top of the plant. So then I could rule out P and see if there's any other issues that would cause edge curling and fading. Those three in combination point directly to a light intensity issue in my book. Looking at your tent it's not hard to see why lol
As far as the red stems and the P connection I've chased that rabbit down many holes and eventually gave up. Without leaf symptoms to back it up it seemed like a fools errand to worry about stem color when the rest of the plant is perfectly healthy.
Those fan leaves up top are definitely taking a beating but that's their job! I would just make sure to keep a close eye on temp up there and check that the top buds are not feeling dry/crunchy. If it is heavy sativa you might have as many as 30 days left to harvest, hopefully less!
but Im happy with the pics too, she is looking good! Buds fattening nicely but yes she is slower. Slower usually means bigger buds though, assuming that the genetics are good and its not slower just because. Runtz does that on me a lot, I buy different ones from different banks and I never know when theyre gonna finish, some are faster but give smaller buds some take more than 2 months but give monster buds, I think it will be a trade off and theyre looking like theyre gonna be big big, as I said before 
