I'm not familiar with the E4801T-9 electrode, but I can tell you this.
If you put a 5/8" weld on 1/4" sheet metal, it will bow and warp it like a rotten banana. Maybe you already realize this and I'm being redundant.
Just in case, here is a handy formula for selecting weld size.
Divide the thickness of the thinner part to be joined in half.
Then add 1/16". For 1/4" plate, that gives you a 3/16" weld size.
You'll need to check the specification you're working from for the minimum weld size, but that formula is usually safe.
Keep this in mind, If you put too large of a weld on the metal, you're putting too much heat and stress into it also. That means that the physical properties of the metal in the heat affected zone will most likely be altered beyond acceptability.
In other words, even if you get it straightened out, the metal will probably crack along the edge of the weld.
Good Luck!