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You have 4.6:1 gears at the moment, 4.3:1 may suit you better but will make the engine work harder so you will "seem" to loose power.
How will it affect off roading - it will be completely stuffed because your front and rear diffs will be constantly fighting each other due to having different ratio's, you MUST change both diffs if you change ratio's. After you've done both diffs it will be the same as on road, the engine will have to work harder.