Comp cams shows the xe284 cam requires 9:1 compression.
What are the effects of using the same cam but increasing the compression to 10:1 ?

 

Is that the 240/246 duration cam? You want 10 to 1 with that cam, 9 to 1 would would have low cranking compression with that duration and probably be a dog. You will need a higher stall and deeper gearing as well.

 

That the one, I'm building a 455 aiming for 10.5:1 compression

 

10.5:1 on what gas?

 

94 octane is available here

 

Good for you. You’ll be fine with that cam and anything above 9.5:1. Just make sure you degree it as per the Cam card. I believe it calls for 4° advance.