Could you help me understand why you have multiple IPs on the same network
using different devices? There may be a great reason, but, in my
experience, it is usually not needed, or can be done better ways using
other technologies (bonding) to achieve business goals (higher throughput
to a box).

Other than that, you could use policy-based routing, I believe, to force
one NIC over another, but I think that's probably overkill. Linux is
pretty clever, so you may even find that if one NIC is down, another on
the same network will magically/automatically be used for data to the
target network. This gets really interesting in case like yours when the
kernel sees any addresses for the entire system as being on whatever
network device, though the details of that mess are eluding me right now.
Anyway, knowing more details of your business goals may help.

Good luck.

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