I have run version 5.0, 5.1 and 5.5 on it, with 16GB RAM and a Samsung 840Pro SSD. The SSD is an an expensive addition, but well worth it.
The RAM cost ~£100 from crucial;
http://www.crucial.com/uk/store/listparts.aspx?model=ThinkPad%20X230&Cat=RAM
I don't see any X230's here at the moment, but I bought a brand new one (with full warranty) from the outlet store for £530.00 excl VAT (less than half price);
http://outlet.uk.lenovo.com/store/lenovooe/en_GB/list/categoryID.56794100
Depending on your location, there is also a US outlet store;
Cheers,
Jon