Just my 2 cents on Priority Mail-
Aviod it at all costs. I bought something from someone on swf.com and I sent payment to them via priority only to have it take nearly 2 weeks to get to them (2-3 days my butt). This is not the first time the USPS has screwed me over either. They treat their packages like doo doo. I sent a CD to my sister and it took over a month to get to her from St. Louis to Wilmington, NC and when it did arrive it was in a plastic baggie from the USPS. They also broke just about everything I sent through them (glassware, collectables, dinnerware) when I moved and the process is such a pain to get reimbursed that it just wasn't feasible.
Anyway to make a long story short if you have to use the USPS, just use regular mail. It will get there in the same amount of time if not faster with regular 1st class over priority. Otherwise I reccommend FEDEX Ground or UPS. for something as small as a 4x4x4 package it's roughly the same as the USPS.
Just trying to help people not get shafted like I did. I think the only priority the USPS has with priority mail is making sure your package gets the worst treatment possible and arrives as late as humanly possible.