There really is no good way to correlate one score to the other. The way CLEP items are graded is based upon the weighted difficulty of each question, which is then converted into a scaled score whose formula is more secret than that of ColaCola and Colonel Sanders' original formula.
Also, the types of questions are very different. Peterson's questions tend to be short and sweet and have only one salient grammatical point to test you on. CLEP questions often require you to note multiple layers of grammar rules and make you read long passages. (I know I just made it sound hard, but this is actually an advantage. This way, there is no question left in your mind which answer is correct since the incorrect ones are more easily weeded out by what facets of grammar you happen to understand best.)
The best advice I can give you to assess your readiness is to assume that you will get every single one of the questions on the listening portion wrong, and see if you can pass on just the strength of your multiple choice answers. I say this because the audio on the CLEP exam is so horrendous that even native speakers can't make out what the heck they are saying. The good news is, it is very possible to get a good score even if you do get all of the listening questions wrong (which statistically is not likely to happen anyway even if all you do is guess) because there are so few of them in relation to the rest of the exam.
BA, Social Sciences (pending final evaluation) ---- Thomas Edison State College
AA, Liberal Arts ---- Excelsior College
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