Yes, you can CF different brands of video cards as long as they use the same GPU (both are 7770).
You only use one CF bridge. Also, both video cards only have a single PCIe power connection.
Last, if your Sapphire only has 1GB of memory, then the Asus will only use 1GB (of its 2GB) when you CF the 2 of them together. Not really an issue, just something to keep in mind.
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