Hold on to your wallets, sports fans, because Comcast is offering its Extreme50 class of upgraded cable broadband in Boston and its hometown of Philadelphia. The service offers 50 Mbps downstream and 10 Mbps up, but will set you back $139.95 a month. A still speedy Ultra connection is a bit easier on the wallet at $62.95 per month; it offers up to 22 Mbps down and 5 Mbps up. For those content to meander along the information superhighway (and maybe avoid Comcast’s cap), Comcast is also doubling the speeds of its lower-tier customers to 12 Mbps down and 2 Mbps up. My 7 Mbps Road Runner is looking awfully pokey right now.