Looking for a particular type of shopping cart for e-commerce?

I am looking for a shopping cart for e-commerce that allows you to bulk upload attributes (size, color, etc). Most of the carts I am finding require the product option or attribute to be installed and then attached to the item. I have over 10,000 items and each color, size, and feature varies by brand - it would take forever to create applicable product options or attributes within the system (trust me - I have already done it with Zulu Cart). Any suggestions? I also want to keep my store front. In general - I would want to up-root from one location and plop down in another within a disruption in business.

Most of the carts I've seen make you add the attributes per product. I don't know if you work with WordPress or want to, but some of the carts I've worked with for WordPress will let you create a set of attributes independent of specific products, though you generally still need to assign the different attributes to individual products. I can't remember if any let you assign a set of attributes to all products or easily assign the set to selected products at once. I want to say some do, but please don't hold me to that.

As far as moving from one cart to another you can definitely do that without disrupting your business. You might have to be down for a brief period when you make the switch, but it shouldn't be long and you should be able to time it when you want. Most systems can be set up in the background so you can build one site without affecting the live site. Switching from one to the other is sometimes as little as moving a couple of files around, though there could be quite a bit of prep work necessary to make that happen. For example one thing you'll most definitely want to do assuming you get search traffic is to make sure all your current URLs are pointing to their equivalents on the new site, otherwise you'll probably lose most of your traffic for a time. As far as moving your data from one cart to another it's hard to know how hard or easy it will be without knowing the specific carts. Some carts make it easy to import and export data. Some don't. There's always a way to move the data though.

Hope something in there helps.