Whats a good amount of Black malt for a dark beer?

[tubthumper]

I based mine on ringwood xxxx porter recipe in grahams book but did this as its what i had and wanted to use up as close to a recipie i could find
3kg marris otter
400g Crystal malt
400g Torrified Wheat
200g Chocolate Malt
and 30g fugals whole boil
then 10g last 10 mins
and 10g post boil
and it turned out verry verry nice no head which is a shame but I havent let it mature in the bottles
it has a lovely coffe choc taste but not over powering
I will definaly try this again and up the choc malt to 300 next time

[WishboneBrewery]

I suppose its good to base things around a benchmark and work from that.