It would help if we knew what your destination was (or where your destination is located). Typically, traffic is heavy on I-4 on the weekends, but you don't get the really sluggish traffic like you do during weekday rush hour. It's heavy, but it moves. The only regular backups I see on the weekends are westbound just north of Sand Lake, around the Turnpike/Kirkman/Universal Blvd exits. For some reason, that area backs up between about 3-5pm every Saturday and Sunday (just when I'm trying to get home from work). But it usually doesn't extend as far south as Sand Lake Road.
You would also want to check the Internet to see if there are any sports or concert events that might cause traffic to be heavier. If you are trying to go up I-4 at the same time people are trying to get to a concert or ball game, it can be a little heavier than usual as well.
You are probably OK to take I-4, but if you can check traffic by phone or online before setting out, it's a good idea.