Ok so do you mean if my goal is to get maximum hypertrophy I should do as many sets of 5 as I can and then on the last set of 5 I can hit drop to the weight from the last session and do 2 sets of 5? I don't think that's what you mean and if it isn't then I think I'm just going to go to option one because in that one either way your going to have to gain strength to hit you goals.
It would be a good idea to experiment with both options, and record the results. Finish this cycle (strength) and then move on to hypertrophy for 6-8 weeks. Each person is going to respond to the same sets/reps/density/volume differently. The key is to find your sweet spot, and stick with it until it stops working.
So far, how's it going with the 5x5, in regards to recovery and gains? I've found for me that a wearing down the CNS with minimal DOMS (less than 12 hours of "soreness") presents my best opportunity for growth. This is why I love a 5x5 scheme, 25 reps is just enough to really tire me out, but not too much as to cause pain.
if you can't do all sets of 5 at the one wt then you can either continue the 5 sets doing whatever reps you can and increasing the total reps each session (option 1) or complete the remaining sets at a lighter ewt so you still get 25 total reps just not with the same wt then again do more reps with your starting wt each session