I don’t have the numbers, but I have seen both. The physical architecture alone should give you judgement. The DL585 has fewer NICs and less redundant fibre channel connections. If you need performance and want to use the NAS for application data (SQL, Lotus Notes, Exchange) then go with the EMC. If you are just looking fo a file server, the DL585 may be a better choice.
In general the EMC gear is oriented more towards enterprise. But if you can afford it, go for the EMC gear, because a small need today is going to grow into a bigger one tomorrow, and you will be ready to scale up or integrate it into your enterprise environment far more easily. EMC has lately been coming down in price as well. So the same hardware with scalability and reliability that was out of reach for SMB is now within the grasp of SMB’s.