Go to your local camera store with your lens and try it out on a camera there..figure out what you want to shoot and just do it...take a memory card with you. That way you can try out a camera that you're thinking of buying.
im in Pomona and have friends in Fontana... im free this weekend but is back to work on Monday... so shoot me a PM if u wanna meet on Sunday morn or afternoon. although, i dont have a d300 or 700... just a d90... IF your OK with that.