Once you're past the OG, the honest answer is that "655+ DI" isn't one bucket, it's three very different beasts (MSR, Graphs and Tables, Two-Part Analysis), and they break down for different reasons. So I'd stop hunting for one magic source and split by question type.
For me the GMAT Club DI question bank was the workhorse, because you can filter by difficulty and by exact type. I'd pull only the 655-705 and 705-805 tagged ones and drill them in timed sets of 4-5, not one at a time. The Official Advanced Questions and the DI Review guide from GMAC are also worth it since the logic style matches the real thing better than most third-party stuff.
One thing that actually moved my score: for MSR and Two-Part Analysis, the difficulty usually isn't the math, it's reading the prompt wrong or missing a constraint buried in tab three. So when I missed a hard one I'd write down whether it was a reading miss or a concept miss. Almost all of mine were reading misses, which no amount of "harder questions" fixes by itself.
If you tell me which of the three types is dragging you down I can be more specific. You've already done the right first step by clearing the OG.
Kavya | GMAT 725 (Q90 V84 DI82), 99th percentile
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