I have been wanting to do a 10.5" build.  But ballistically, according to this chart I don't see a significant difference between the 10.5" and 8.5".  Is this data inaccurate?  Anything else to consider?  I only ask because 8.5" is readily available.  

Also, functionally....any downsides compared to a 10.5"?  Maybe a massive fireball out the end vs a 10.5" that might now have it....a lot louder vs. the 10.5"....etc. etc....??

Thanks!

I reduced the fireball with my 7.5" with hand loads using H322... blast with a LeVang linear comp on the 7.5 is similar to blast when compared to a flash can on the 10.3 with M855 from shooter's perspective

2 inches makes a little difference in velocity but neither 10.5 or 8.5'' is optimal anyway.
As far as reliability the 8.5 will use a pistol length gas system and have about 1'' more distance between the muzzle and gas block hole in the barrel.  The longer distance will be an advantage for the 8.5'' during cycling but overall length is an advantage for 10.5''. Either can be made to work fine.
The blast is big with either but the 8.5 will be a bigger blast. Both can be tamed with the best flash hider and blast forwarding device you can get.