Have you killed anything with the Fed 2 3/4" yet? If so, what, how far away, and how was the expansion/devistation? Also, are you shooting the 1 oz or the 3/4 oz slugs? I will try these at the range ASAP since OH deer season opens in less than two weeks.
I'll have to try the barnes 2 3/4". Like you, I've tried ALMOST every slug. So far the best I've found have been the Winchester Partition Gold, Winchester Platinum, Lightfield Hybred EXP, and the Hornady H2K Heavy Mag. All shot 2-4" groups at 100 yards, with the Lightfields being the most accurate. The least accurate have been the Remington Core-Lokt and the Lightfield Commander 3".
One thing I have done to help imrove my accuracy is have my trigger adjusted by Allen Timney. He took out the creep and reduced the pull down to three pounds. He only charges $65 and covers it for life.