The various body fat % testing methods have varying degrees of unreliability ... and the results are very easily miscomputed or misinterpreted. How "professionally" are the tests are conducted? Which (of many) formulae are used to interpret the results? The results can vary widely. Above all (IMHO), what's most important is HOW test results are used to modify training and/or dieting.
First, ask yourself WHY you want to know your % body fat. If it's to compare to other vaulters, then you may already be on the wrong track. There's just too many variables to make this a useful comparison. Better to compare your % body fat to YOURSELF over time ... perhaps monthly. If you really want to compare yourself to another vaulter, compare PRs. Nothing else matters.
Second, how accurate do you really expect the test to be? A 4% fluctuation from one test to the next is quite common, meaning that any % less than this is insignificant ... and should be disregarded.
I like the KISS principle ... which applies to computing % body fat (as well as many other things in life). If you're training to be an astronaut and your fitness if mission-critical, then sure ... take a complicated test ... but if you just want to see if your % body fat is increasing or decreasing over time, use one of the simple "body circumference" tests ... either the YMCA test or the Navy test. Actually, they're both quite simple, so I'd do them both ... and compare the results over time. Even just by observing the variance between the 2 tests, you'll expose their inaccuracies ... reminding you not to over-analyze the results.
You'll find them both here
http://fitness.bizcalcs.com/. You'll also find a couple of skinfold tests here, but personally (even if I had the calipers), I wouldn't bother.
Don't just take the circumference tests. Record them in your training diary, set an objective on what you want your ideal % body fat to be (or your raw girth measurements), and take ACTION in your diet and training to try to reach your body fat goal. KC, you say you vaulted your best when you lost about 10 lbs and about 3-5% body fat. So all you REALLY need to monitor is your WEIGHT. Since there's such a high correlation between weight and body fat (for your specific height, body frame type, and metabolism), you know that any loss of weight will have a corresponding loss in body fat. KISS. Sorry I'm not answering your specific question about diet. Just eat healthy foods.
Kirk