So whats the Dilemma?
Have you already got both sticks purchased? If so, why dont you just swap them in and run a few tests, then try the other set?
If you are wandering what to buy between the 2, then it depends what you are going to be doing. To be honest, you arent going to see a huge difference between 533 and the 800, unless you are overclocking.
If you already have the two, I would be going for the 833. If you are looking to buy either of them, I would get the cheaper of the two if there is much of a difference in price.
Just out of interest, what is the 2GB of 800, 2 x 1GB sticks, or 1 x 2GB stick? Hows the 3GB coming? 3 x 1GB sticks? Just make sure your MOBO supports it, if you are using 3. If you are buying, with an upgrade in mind later on, might be useful to know. However, DDR2 RAM isn't the way forward, so keep it cheap if you are buying.