The Slam attach action listed in the combat chapter of the core rules says that you gain either a +2 or +4 based on move action and add your Speed rank if you can move the minimum distance (100 feet for rank one, and progressing normally alongside.the speed rank value essentially)

If I'm a speedster.who uses Slam, is my total damage limited by PL like normal? Do I take a penalty to compensate for higher damage?

Damage and Attack values are always capped by PL, the same way Defense and Toughness are.

That is simply not so.  There are numerous things that skirt around the PL limits:

• Extra effort
• some feats (Power Attack, All-out Attack, etc... although some other feats, such as Sneak Attack, do specifically state that they are limited by PL)
• critical strikes (which can be bought up to 'automatic' if you take enough levels in the feat)
• maneuvers and modifiers (Combined Attack, Slam, Aggressive Stance, Autofire attacks, ganging up)

Slam has its own limitations - like requiring a full move action in a 'relatively straight line,' the possibility of taking damage yourself when you use it, and the fact that your Strength bonus doesn't add to it - that can keep it in line.

That said, if it looks like it could be a problem with a particular character, talk to the player and come to an arrangement.  Just because the character can do something by a strict interpretation of the rules doesn't mean that the GM has to allow it.
This message was last edited by the user at 14:42, Wed 07 May 2014.