The suggested "limit" on polygons is 1 million, so if you meant 75,000 or 750,000 you're still well under the "limit". The actual limit, however, is how much can your system support. The faster your processor and the more RAM you have, the more advantage you have. Version 3.1 is more stable at handling large numbers but even there, the same kind of "limit" applies (relative to system support), although performance difficulties are more noticeably related to higher bytes rather than polygons. You can try out the v.3 demo to see how it works without having to upgrade to it. :)