Observable Relativistic Effects in Astronomy?

According to the HyperPhysics site, super novae are detectable out to
8 billion light years. And according to Hubell, super novae at that
distance should have a velocity relative to earth of 0.6c. This would
result in a relativistic time dilation factor of 1.25. Consequently,
the average of luminosity curves of super novae at 8 billion light
years should be stretched out by 25% as a result of relativistic time
dilation, when compared to closer super novae. Is there any data
demonstrating this?

Also, is there any detectable difference in doppler shifting of light
from the receding arms versus the advancing arms of galaxies at 8
billion light years distance? If so, is there any difference in the
mean rotational velocity of a large sample of galaxies at 8 billion
lys and above, versus, a large sample of 1 billion 2yrs and below?

Thanks,

Pat