I like the 500 idea, because when i think of 300 I am not intimidated. When I think 500 I am thinking I better get my sh... together and ride. Having a goal really keeps me motivated. One of my current goals is to get my 60 mile ride done in 3 hours or less. I am currently at 3:35, but it is about 20 minutes shorter then in Dec.
Also I've lost about 45lbs since August. The lbs are coming off slower than at first but that is natural. I weighed in in the 270's today for the first time in about 10 years. I still wanna lose another 100lbs. I know that is gonna take a lot of blood, sweat, and more sweat.