Rob
The Summit is a higher spec'd model, higher BTU out put and a little easier to cook on without having to do too much seting up for indirect, The Summit is deeper but narrower. Does it come with the SS rods - they are my choice over PCI, however I know many on this board may disagree. I like them as they hold the heat just as well as the PCI but are much easier to keep clean and release the meat easier.
Both the Summit and the Genesis are wonderful to cook on and will out last most others on the market.
It has been my experience that most owners of high end BBQs change them jjust to get the latest model not because the BBQ is broken whereas the cheap models are discarded because they are broken or the owner is sick of the BBQ not producing the results that the owner would expect out of a BBQ.
Regards