Shopping Cart Feedback (specific carts)

Hello all, I currently maintain www.affordable-solar.com We have our own managed server and are looking to switch / upgrade shopping cart / cms. Right now we have a customed designed site that does both of these, but there are alot of reasons we want to switch
-no documentation
-only support is from the company who made it
-many features lacking
-lots of manual maintenance

I have been looking at many different shopping carts and am looking for feedback on specific ones that seem like they may work well. Features that are very important are the following:
-built in support for real time shipping rates + some real time freight shipping quotes.
-support large number of products, at least 10000.
-be able to create custom fields at least by product category. For example all products in solar panels should have a wattage field, while another category could have voltage. The purpose of this is to compare products such as x-carts x-featurecomparison add on. Also, we would like to be able to list products by custom fields as well..for example you click on a voltage link or drop down at the top of the page and it would sort all products in that category asc / desc.
-Some sort of image filing system so you can easily re use images on the site such as using product images in learning pages without manually using imgage tag or using same images for multiple products.
-Editing multiple products at the same time by different filters, such as category. ie. mass price updates.
-copy product feature - to add a similar product and only change a few attributes.
-seo friendly
-Product categories can go at least three layers.
-Easily change look with template based layout.
-good CMS system for knowledge base / faq with good linking / breadcrumb system. For example all learning pages about a certain category would be displayed on that category in a resources box - all database driven and easily editable
-offline cc processing!
-different checkout options - speedy checkout (1 step)
-good customer options such as wishlist, ratings, etc..at least be able to add on through modules
-good bulk product import export
OK big list i know...but those are some of our primary needs! I've been looking at many and was looking for feedback about some specific ones:
--xcart: seems cheap and good add ons. Also our site now uses smarty templating system so i would be familiar with.
--zen cart: many options and add ons - free
--CRE Loaded + Content Director for cms - seems to be one of the only carts with a decent (easily added and designed to work with each other)cms which is important for us.
--OS Commerce-free and many add ons.
--joomla w/ virtuemarket- Joomla mostly for easy add ons and great CMS.
--CS cart- have seen alot of good things about it on these forums...but is there any cms?
--Shopsite- got best reviews on shopping-cart-review.com, but demo'd back end and it didn't seem very robust.

Ok so any feedback on ANY of those carts would be greatly appreciated, based on what our needs are. Also is shopping cart a good solution or is custom built better. I have some knowledge with mysql php and web design so we want something that I can update / add new features with add ons and modules. But maybe this is not the way to go? Thanks again for any input.

Since CS-Cart is developed by some of the same folks who were involved with X-Cart I would choose the former. I use it. CMS can be handled by the page manager feature and you can edit an .ini file to create your sort by category. I have added a shop by price feature on my vitamin site this way. Several layers of sub-cats are standard as well. The rest of your needs can be implemented such as anonymous or quick checkout, off line credit card processing, wish list, ratings, etc.