Hey,

The quantitative ability in CAT is relatively more difficult when compared to GMAT or GRE. CAT require the candidate to select only one answer for a question, GRE requires the candidate to select multiple answers or type-in an answer in certain question types. GRE is a section adaptive test - the level of difficulty of one section depends on the overall performance of the candidate in the corresponding previous section whereas CAT is a linear Computer Based Test. CAt is a bitmore tougher overall when compared to GRE. But GRE requires practice in verbal part alot.

If you prepare extensively for Cat, you can do well in GRE as well. Taking both these tests side by side is generally advisable for college students preferably in their third year.

Hope this helps.