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Oracle also supports the SAMPLE syntax similar to TOP in T-SQL. In either case, the difference is in syntax. I haven't tested it but I would guess that TOP versus a nested query would produce the same execution plan. I'd like to hear it if that is not the case.
The performance impact would be depend on the level of complexity of the inner query. If the inner query matches all specified conditions, retrieves 3000 records, sorts these records on created date, and returns just 100 records, performance would be bad. In this case, you may consider creating new index to reduce the performance impact