IMR 8208XBR, AR-Comp are good powders for the 6.5g though 8208 will deliver slightly better velocity. I've never tested it with CFE223 since it was not out yet back then. I now have some and its on my to-do list. BTW, Lapua brass lasts a lot longer than Hornady before the primer pockets get loose. A.A brass is actually rebranded Lapua and they used to have it on sale occasionally. (I stocked up)
My 2nd Gen 6.5g is a tack driver with the now discontinued (I stocked up) Hornady 123 Amax.
8208XBR
AR-Comp
Those were shot with 24" E.R. Shaw production overun barrel made for Alexander Arms about 10 years ago. They were sold for a short while on Midway under the AR Stoner product line back then. One of those being in the right place at the right time opportunities. This was and remains my most accurate AR rifle. It likes 120 NBT but not as much as the 123 Amax.
I have no experience with the new generation 6.5g. FYI, the 2nd gen has a deeper bolt face and compound throat as originally spec'd by A.A.
Hoot