I used a teaspoon of spice a few years ago, you could taste the spice, but it was subtle. I wanted to bump it up last year, so tried a tablespoon of spice and it was a little overpowering, totally masked the pumpkin (all 5 gal batches). This year I went with 1 1/2 teaspoons, but it is still aging, so haven't tasted it yet. I add the spice when the primary fermentation is winding down, but still moving the beer around; seems to do the trick.
I use Fuggles and EKG, around 25 IBUs, and I do add small late additions for aroma and flavor.