750 Necron All-Comers

My local game shop is hosting a 40K tournament which will be a great opportunity to see how the new Necrons play against lots of different armies. This is an all-purpose army I came up with:
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Combined Arms Detachment:

HQ
- Catacomb Command Barge (warscythe, phase shifter, gauntlet of fire)

Troops
- Immortals x5 (gauss)
- Immortals x5 (gauss)

Fast
- Destroyers x1
- Destroyers x1
- Destroyers x1

Heavy
- Doomsday Ark
- Heavy Destroyers x1
- Heavy Destroyers x1

Total Points: 750
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The gameplan is to have the CCB race ahead and assault the big things (monstrous creatures, vehicles) while the Ark takes out larger groups. The Immortals provide a strong core of gauss fire which can kill most non-marines easily and also glance vehicles to death. The Destroyers can capture objectives and take out more heavily armored foes.

I'm not sure about the heavy destroyers. They have good range but at 750 I feel like maybe scarabs would be a better choice. I wanted to take tomb blades since they're ridiculously good in the new codex but unfortunately they're super expensive (and no proxies allowed).

Any advice is welcome