Just checked at USPS.com and yes, both the 3" longer legal size and the padded letter size ship at the same $4.95 rate as the letter size flat rate envelope. You can even buy prepaid "forever" postaged packs to be ready for the next rate increase. To stuff in more, though, how about the small flat rate box? It only costs 25 cents more than the enevlope.... All have a maximum weight limit of 70 pounds, and even lead melted into a just-fits block would weigh less than that.