I have solved 1000series and from my experience it is definitely around 650-680 level except last 2-3 questions of every set that tend to be 700 level. 1000series helped me a lot in word problems, be it mixture,ratio,percent,interest or any other. I was getting bogged down by wordings but this question bank really helped me figure out word problems really quickly. I have solved most of the set and at one stage I could solve all question much within stipulated time. That's the key. But do not expect tougher mean-median or geometry or inequality questions from these sets.
For 700-level, check out GMAT Paper Test sets. That's very close to real GMAT exam except well it is not CAT.
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My dad once said to me: Son, nothing succeeds like success.