Hi Christian,
at http://service.sap.com/erp-ehp you can check the differencies of the business functions.
Click on "All business functions in detail" to check which functions have been delivered with which EHP.
Technically EHP7 is based on SAP Netweaver 7.4 (SAP_BASIS 740, SAP Kernel at least 740)) and EHP6 on SAP Netweaver 7.03 (SAP_BASIS 731, SAP Kernel at least 720_EXT).
Cheers,
Andreas