A 720+ GMAT score is useful for parallel ISB applications but doesn't directly translate to CAT success; CAT requires its own strategy and preparation. GMAT and CAT test different skills: GMAT emphasizes verbal logic and problem-solving under time pressure; CAT emphasizes raw speed, trap-avoidance, and sectional strategy. The OP of this IIM Mumbai thread said past GMAT papers are useful for VARC practice specifically, not for CAT overall.
GMAT score helps for: ISB, US top 10 MBAs, MIM programs in Europe and Canada. CAT score opens all Indian IIMs plus new IIMs, with no overlap with ISB/foreign MBA. For GMAT-primary candidates, switching to CAT requires 3-6 months of dedicated sectional practice plus mock series.
CAT VARC is more literary and tests RC reading speed; GMAT VARC is more logical and tests critical reasoning. For QA, both are similar at intermediate level but CAT emphasizes calculation speed. For DILR, CAT has set-based logic; GMAT has pure critical reasoning.
Don't bank on GMAT preparation covering CAT; do dedicated CAT prep with past papers. Check your eligibility at collvera.