I am now over the 15% of top MPR and I was going to buy some BA before the cache flush so I could get more XP out of it, as stated below from the wiki, and I was wondering when the cache flush was. That way I could purchase my BA at the right time.
"[I just verified this. Rate is based on MPR, not VPR, and is only evaluated during cache flush. So yes, you can buy your BA right before cache flush if you are on the verge, then spend it all at the higher rate. ~NightStrike]"