So I called them up. I asked about prepaying some or all of my upcoming purchase. They transferred me to a special division that deals with the spending limits. Rep said he would check to see if an 86k charge would go through...and it did! I was pretty surprised, considering it turns out my "credit limit" is only 23k. Anyway, it looks like I'm all set, at least for now. Unfortunately, I've used up all my miles earning ability on this card for next year...on the first day of the 2008 billing cycle/year no less!