So, one week (and 6 pages) ago I started my investment experiment, costing my family 210 gold. The advisers had expected a 190 gold return. Here are the results:
Stats Prior to Investment:
Region Tax Report (8 hours, 12 minutes ago)
message to the lord and knights of Nifelhold
The following taxes were collected in Nifelhold. The tax rate for this collection was 14 % and the lords share was 10 %.
Regional income and expenses
Peasants Taxes 246 gold
Taxes from Guildhouses + 1 gold
Buildings Upkeep - 10 gold
Militia Payment - 46 gold
Collectable Tax Gold 191 gold
Estate of Size Peasants Tax Collected Knight Share Lord Share
Walter 40 % 2520 76 gold 68 gold 8 gold
Rohk 36 % 2268 68 gold 68 gold
Wild Lands 24 % 1512 22 gold 22 gold
Region Totals 166 gold 68 gold 98 gold
Stats After Investment
Region Tax Report (6 hours, 51 minutes ago)
message to the lord and knights of Nifelhold
The following taxes were collected in Nifelhold. The tax rate for this collection was 14 % and the lords share was 10 %.
Regional income and expenses
Peasants Taxes 458 gold
Taxes from Guildhouses + 5 gold
Buildings Upkeep - 10 gold
Militia Payment - 45 gold
Collectable Tax Gold 408 gold
Estate of Size Peasants Tax Collected Knight Share Lord Share
Walter 40 % 2520 163 gold 146 gold 17 gold
Rohk 36 % 2268 146 gold 146 gold
Wild Lands 24 % 1512 48 gold 48 gold
Region Totals 357 gold 146 gold 211 gold
Results
Personal Income: +113 gold
Knight's Income: + 78 gold
Total Return: +191 gold
Conclusion
1) Advisers do take into account your current tax rate when deciding the return on your family investment.
2) Family investments are not a lucrative use of family gold. I would likely be more efficient to ask my family for gold on a weekly basis and then bank it or place it in a guild. I effectively lost 20 gold through this transaction.