AGI has a much larger impact than just 4%. I have base 300AGI, thats like 35% avoidance. Turn on def stance it jumps to almost 60%. I dont think it can go much higher than 60%. At 500 AGI, my avoidance doesn't reach 70%, so if you are already capped it probably wont affect avoidance very much.
Half-elves are the best IMO, good mix of primary stats. The extra STR from the human and extra AGI from the elf. Humans do not get bonuses to STR, but theirs is higher than an elf.