Fairly cool, given how high the values of coin we’re told we receive, I would think a lesser value coin would be more authentic.
In the GameOfThrones universe 4 gold-coin is basically a suit of armour (http://awoiaf.westeros.org/index.php/Currency). Which in George’s universe equates roughly 800 silver or 6400 copper/something.
Although in the tv show 8 barrels of Dornish wine are bought for 100 gold, and for a nobel melee contest 20,000 gold is on offer (5000 suits of armour). But that takes place after a long summer in a more heavily populated setting.
I think given the early medieval setting, doubling those amour costs so that a good suit costs 1600 silver would work, but at that point devs might as well just use the current gold values for silver instead.