My best results have been with JSB Jumbo Exact Heavy (18.1 grain) out of BSA S10 barrels running the pellets at approx 881fps (31FtLb) giving sub 1" groups at 100 yards.
JSB Monster and H&N Baracuda didn't even approach 1.5" group size under same conditions.
I have no idea how well the Sumatra barrel may like these pellets as I've never tried an FAC Sumatra but a sub12 .22 Career was pretty good with JSB Exact and Exact Heavy at 50 yards.