Ok, first off when it comes to the 6.8spc you need to know that there are 2 chamber designs. Like the 223 and the 556. 6.8SPC is a very weak and under performing load, remmington messed up the chamber design, this pattern is almost completely abandoned and only a couple of companies still use it in their rifles. The other is the 6.8SPCII, it has the correct leade and freebore, and can shoot a much hotter load than its little brother the 6.8SPC. Most all published reloading data is for the SPC, and using a 24" test barrel. For 95 and under bullets Reloder 7 works best, 95-120gr bullets Accurate Arms 2200 is the powder of choice, for 120+ H335 seems to be the ticket.
My reloads are as follows:
95gr Barnes TTSX, 30gr of RL7, CCI450 primers, SSA brass, 2.295 COAL. Produces 3/4-7/8" 100yd groups, at 3050fps.
100gr Nosler Accubond, 28gr AA2200, CCI450, SSA brass, 2.295 COAL. 3/8" 100yd groups, 2845fps.
90gr Sierra HP, 29gr RL7, CCI450, SSA brass, 2.285 Coal. 2950fps and .2-.22" 5 shot 100yd groups. SUPER ACCURATE
140gr Berger VLD, 27gr AA2200, CCI450, SSA brass, 2.295 Coal. 2450fps 1/2" 200yd groups
If you are interested in getting a 6.8, go over to 68forums.com and look around for a little bit. Check out the stickys, there is some great info in them!