A 3300 is an older cell than a 4600 of course. There are a couple of things I think that people are slightly mistaken on or perhaps just didn't explain it clear enough.

A good matched 3300 can hold just "as high" of voltage as a good 4600. The peak voltage before it levels off is about the same and lasts for about the same amount of time given the same draw. The difference however is the amount of time that the larger capacity battery (4600) will have that level power. It is longer of course.

There is also a big difference in weight.. the 4600 for its higher capacity will weigh more... thus slowing the car down. This you really can feel when racing.

Now.. with all that said... if your batteries are old and used back when they were the newest cell out.. well.. go for new ones.. You'll more than likely need them anyway.

Good luck!

Jerome