Definitely do 5 lbs - that's actually 300 lbs in 20 weeks or 600 lbs in 40 weeks while diong SS (+15 per week).
There's no reason to continue doing 10 lbs. Being greedy will just make you stall quickly, be forced to reset and work your way back up in 5's anyway. Save yourself the trouble and drop to 5s now.
Hell I think most people drop to 5's at like 200 lbs lol. Besides you've already failed a weight, are you really that eager to continue missing weights?