So I have a strangth of like 1600. It is nice to be able to carry lots of stuff, but killing people is never a challenge. I increased my strengh with the sunder cheat. How can I return to normal or reduce it?

The easiest solution I can think of is to create a powerful Damage Strength on Self spell. That could do the trick.

won't it just come back with time or sleep or potion?

Only with a restore strength potion or using a temple shrine. Once damaged, waiting or sleeping can't bring it back up.
There might be a few other ways you'll get your super strength back, but you can always cast your spell again.

Open the console, click your character, and type:
setstrength X

X being whatever you want your Strength stat to be. This is, of course, assuming you're playing the PC version. If not, go for the solution provided by Logorouge.