Tested in Anguish solo exp with level 77:
1,000% = 15 AA
2,500% = 36 AA
5,000% = 30 AA
10,000% = 19 AA
25,000% = 25 AA
Seems we have a roll over between 2,500% - 5,000%
Best bet is that it messes up at 4096 or around that "magic" binary number... 2 4 8 16 32 64 128 256 512 1024 2048 "4096" so 12 digit register -1 for signed, would have had issue after the 5,000% if it were unsigned.
Or something like that...
If so, then the best you can do is a 4,000% item