Hi gmat730must,
On Test Day, you're going to be in a computer lab with a number of other Test Takers. That type of environment is tough to mimic, but a computer lab at a public library might similar enough. Barring that detail, you should look to make the experience under which you take each CAT 'match up' in as many ways as possible with the experience that you'll face on Test Day (FULL CAT - with the Essay and IR sections, time of day, travel time, general testing environment, etc.).
1) How long have you studied?
2) What materials have you used?
3) How have you scored on each of your CATs (including the Quant and Verbal Scaled Scores)?
4) What is your goal score?
GMAT assassins aren't born, they're made,
Rich