I have not always been nice to WPMUDEV - some acid comments about the Membership plugin - but I wanted to say I am impressed by the performances of the MarketPress plugin.
I did a test comparing the Woocommerce & MarketPress plugins, exact same setup, same number of products, plugins, widgets on pages, same content overall, etc - I cloned the site with the Duplicator plugin by lifeinthegrid.com which is free and fast (Sarah Gooding wrote a post about it somewhere on wpmu.org, check it out).
The results on a localhost setup with no caching.
Average # of SQL queries per visit went down from 80 (avg.) with Woocommerce installed to 50 (avg.) with MarketPress.
Plugin load time for MarketPress was four times lower then for Woocommerce, from almost one second to 0.2 second.
Memory usage was down from 64 Mb to 60Mb, which isn't negligible either considering that is just for a single plugin change.
Tests were repeated five times, to be sure.
Won't go into details (I used P3 - Plugin Performance Profiler, check for yourself, it's a free plugin, good enough for preliminary tests) but I must say these are good results.
Market Press automatically imported products created with Woocommerce.
Works with the Genesis framework without the need of a connector plugin (minor css tweaks only).
I have always used Woocommerce for clients so far but I think I might give MarketPress a try.