Shopp (shopplugin.net) can handle as many products as WordPress can posts, though I think the same could be said of the other solutions as well (WP e-commerce, Jigoshop, WooCommerce). They all also have support for handling shipping and taxes.
Your mileage will likely vary greatly in terms of how well any one of them will fit your exact workflow and needs. Shopp has integration with TaxCloud (taxcloud.net) so you can outsource your tax collection problems for all 17K+ tax jurisdictions in the US. Shopp also has complete integration for ShipWire (shipwire.com) to outsource order fulfillment and warehousing/inventory. If you want to take care of fulfillment and inventory in-house, you can still do that as well. Most of the stuff to do that comes with the plugin. Hope it gives you at least some good guidance.