8208xbr is a fast powder not close to h4350. I personally wouldn't use it in the creed even with the lightest of bullets. It is better matched to the Grendal type cartridges and varmint cartridges. My $.02
Hodgdon lists load data 6.5 Creedmoor loads for IMR 8208 XBR from 90 grain to 140 gr bullets on their website. http://www.hodgdonreloading.com/
The velocity for light bullets is equal to other powders listed. With 120 and heavier bullets the velocity falls off a bit. With a 140 it is the slowest powder listed with velocity of 2511 while the most of the other powders are 90 and one (4450) is 160 fps faster.
I use 8208 in my 308 with 168s for a super accurate load with somewhat slow velocity of 2500 fps. It really shines in my 6 BR with 105s but again it is tad slow @ 2825 fps. BUT it is very very temperature stable something I like as I live in S. Az.
I tried it several years ago when Varget was hard to find. I read about it on Accurate shooter, tried it and never tried any other powder after that.
I would say if you have some give it a try, think you will be pleased with the accuracy and temperature stability.
That really depends on which bullet and weight you are using, i.e., 140-143 ELD-X. According to my Hornady 10 ed, 36.4g of Varget gets you at ~2600 FPS and 44.7g of Superformance gets you ~2800 FPS (24" 1:8" 210M hornady brass 2.825").