I think HP5+ @EI 6400 is going to be rather hopeless, especially in D-76. While you could certainly get an image, it'll be extremely harsh and grainy. But if you insist, around 30 minutes at 75F would be a starting point.(posted 8592 days ago)If you really want a halfway decent EI 6400, try Delta 3200 in Microphen, 13'/75F.