Magento or OpenCart or ??

Hello,

I am currently considering taking on a client who needs an ecommerce solution built for his online furniture sales business. He has over 4,000 products and would like the following features:
Discount Vouchers / coupons
ability to filter products by various attributes, such as price, style, colour, etc
custom freight module
wish list
datafeed for google cart
maximised SEO (who doesn't?)
warious discount options
related products
high-end search with search suggestions, product match selection list as user types, etc
and various other features
Unique, stylish design
various other requests

I am writing up the Requirement Specification and want to outsource the front-end and back-end development part of the project. I am considering OpenCart or Magento based on my initial research...
Can anyone give me a fairly detailed comparison of these or other recommendations for other ecommerce platforms with reasoning to aid me in my decision for this case scenario?
Items such as available off-the-shelf features, ease of development/cost of development,server requirements,forward compatibility/upgrade options, initial cost, speed of operation, and so forth will help me make up my mind.

Many Thanks...