The eighty minute tapes use a thinner tape stock making it easier for the tape to tangle in the heads or to get dropouts. If the project is of any importance I'd stay away from the 80s (Panasonic states that you shouldn't use them right in the manual).
If you're getting paid for the project, I'd recommend using the AY-DVM63AMQs. If you can save yourself one dropout at an inopportune time the extra couple bucks is well worth it.
Besides, most clients will reimburse you for the cost of tapes.
I just found a site www.tapestockonline.com that you can get the DVM63PQ's for $3.99 each when buying 1-9 of them. If you buy more than $25 worth of stuff and use the code "P25" when you checkout you can get free shipping.
I'm about to order a bunch of them...I'll post back in here if it's a bad deal or not. I've never bought from them before so I can't speak on their business practice but haven't seen anything negative on them.
It's been 5 days since I placed my order...got my initial confirmation, and the money has been processed..here's a portion of said email...
"This email is to confirm the receipt of your recent order from TapeStockOnline.com. We will email you your tracking number the evening of the day your order ships. Most orders ship the day the order was placed, if placed before 4:30pm Pacific. Our acceptance of your order is subject to availability of the products ordered and the verification of your payment. See http://www.tapestockonline.com/info.html for more information. If you do not receive a tracking number within one business day, please feel free to call us at +1 (310) 352-4230 and ask for the status of your order."
I never received the tracking number or a call back, BUT, I did get my tapes today. 7/31. Poor communication but 6 day turn around on free shipping is OK by me. B&H charges a bit less per tape but you have to pay for shipping. I figure I saved about 10%. I'll buy from them again.