Well guys it's been over 4 months since I wrote that and I've completed a big ebay push selling all the stuff we had been hoarding in the attic and some other things and I can say that over about 60 or so sales/shipments USPS was the cheapest option for about 55 of them.
I don't like the post office's policies on things too much, but they are offering an exceptional value compared to UPS/fedex. Unless the item was under a pound I checked every package usps vs ups/fedex and nearly always usps was the better price. Generally speaking I'm finding that UPS/fedex only win when it can't fit in a flat rate and is large or heavy AND shipping over half the country away.
I think the big companies must get an exceptional rate from ups/fedex when they use them, or they are just easier to deal with professionally than the P.O.. For us little guys the post office generally seems like the way to go for most reloading size items.