Is there a reference for these kind of questions?
I found this:
40- Sweet, caramel, toffee — Drum roasted, crystallized malt; improves foam; enhances viscosity; golden hues
60- Sweet, pronounced caramel — Drum roasted, crystallized malt; improves foam; enhances viscosity; deep golden to red hues
80- Pronounced caramel, slight burnt sugar, raisiny — Drum roasted, crystallized malt; improves foam; enhances viscosity; red to deep red hues
In short, it helps to taste each grain before composing a recipe with it. Pop a fair amount of it your mouth and chew it up a bit. Keep in mind that a lot of crystal adds a sweetness that is (IMO) not desirable. It's rough to brew 5-10 gallon experimental batches in this context (because that's a lot of beer to drink or toss), so I try to brew 1-2 gallon experiments to dial it in and then ramp up.
I think that's a lot of why I prefer UK crystal malts overall. Much broader flavor.
+1 to what Sean says. Again, taste it first. Next step would be thinking through percentage usage and at what ABV you are shooting for. It's easy to go over the top.