WRT the exercise profiles: different types of exercises are tracked differently by the watch in terms of caloric burn and feedback to your computer. These watches hookup to you computer and database your workouts so you can track the effectiveness of your workouts and set goals, etc. In the case of the 305 (and I believe the RS800 although I haven't tried the feature) you can upload running routes (you may or may not use this) to the Garmin community and anyone in the area can use that run route. You can compare run times and set up a competition, etc. For weight lifting, you can track your workout by time and effort levels, and program workouts requiring you reach a heartrate and maintain that heartrate for a period of time. Works well with weight lifting, or strength exercising like crossfit.
I hope this all helps. You can download the user manual for each to see what they can do for you. Good Luck! Let me know if you have any other questions!