A more upright position will easily accomodate any extra weight you carry around the middle. Just don't worry about speed for a long time yet, enjoy riding and the scenery! People will pass you all the time. As you lose weight and gain fitness you can start thinking about a bike with a more forward-leaning position, if you want to go faster. But as I read somewhere - there's always someone out there who is fitter and faster than you, so there's no point in worrying about it. Riding slowly has its own special value.
Winter riding is much less about badassery and much more about bundle-uppery. - malkin
1995 Kona Cinder Cone commuterFrankenbike/Selle Italia SLR Lady Gel Flow
2008 white Nakamura Summit Custom mtb/Terry Falcon X
2000 Schwinn Fastback Comp road bike/Specialized Jett