None that I can see, except for ammo for both. Make your choice and stick with it.

The 6.5 has ammo available from Alexander Arms (spendy) and Wolf.

The 6.8 has ammo available from SSA (Silver State Armory) in Morton, WA, as well as Remington and a few others. SSA brass is small rifle primer, Remington brass is large rifle primer. (Two formats is confusing, make sure you sort brass correctly.) No Wolf available.

Both calibers have a lot of projectiles out there, with the Barnes TTSX being some of the best ones IMHO, Accubonds coming in a close second.

I have also been able to find Remington 115 FMJ's, so I bought 3,000 for the 6.8 SPC. (6.8SPC was developed to be a replacement for 5.56x45) Lots of bulk projectiles available.

6.5 FMJ's are SPENDY, so be prepared (Lapua). Cheapest ammo by the box is $13 for Wolf through AA. Don't see any loaded FMJ offering by anyone. Pretty expensive blasting/training ammo. Not a lot of bulk projectiles available.

I handload everything, so I bought 1,000 pieces of brass from SSA. Relatively low pressure round, so the cartridges don't get too beat up. Easy round to load, good accuracy, and the boys have taken 3 deer to date with our 6.8.