If what you say is true you are doing 8 reps above 90% twice in 8 days? That is a bit too much and may be overtaxing your CNS. Prilpin's chart usually recommends 3 to 5 reps at or above 90% of one's max for increasing strength. If you're hitting it like this every fourth day then you're not giving yourself any time to adapt. Try working up to a 3 rep max or a heavy double once a week. More is not always better.
If you're able to handle this kind of volume now, why not try for a new max? Why wait until November?