MSPHUNTER,
Consider the Leupold 4.5-14x50 A/O. Here's why. What does the 3.5-10 have that the 4.5-14 does not? It has 3.5x and there's not a lot of difference between 3.5x and 4.5x. Now, what does the 4.5-14 have that the 3.5-10 does not? It has 11x, 12x, 13x and 14x. These are the powers that you will most likely be using with a .338 at 300 yards.
Also consider a 50mm objective if you go with the 4.5-14, it gives you a larger exit pupil that you will need on the higher powers.