I cheated and used the app on my phone, I came up with only 1.12% drop using 3/0 conductors. This is calculated at a full 100 amps. My first move would be to determine actual load on the panel, then calculate from that as it would reduce wire size. As for the wire size exceeding 4/0 just go bigger, or run paralells. On paper it all looks good but in the field you will have a tough time finding a 100 amp panel with lugs big enough to accept a 3/0 wire. In your example #3 copper is the correct size for the specified ampacity, but it is a little over your drop spec at 5.67%, so looks like one size up would do it for you #2 comes in at 2.37%.
Life is tough, Life is tougher when you are stupid