Frank, I personally tend to worry less about the weight and more about the density. In other words, you can have a heavily weighted nymph with a lot of bulk that will sink slowly, and conversely something like a traditionally tied Sawyers PTN will sink quickly despite being relatively light. Then there are other factors, such as the tippet its tied to. Some tippet materials are quite dense and sink quickly, others not so, not to mention how think a tipet material your fishing and if its inadvertently been coated in floatant. In my opinion the only way to know is to tie your rig up and plop it in the water a rod length up from you and spot what depth it gets to by the time its at your feet. I pretty much do this every time I tie a nymph on.
The number of times iv fished with someone and they claim a fish isn't feeding after they have cast to it multiple times, then I get them to drop their rig in the water a rod length up and the nymph is only sinking 4" when the fish is lying at 2'
Also I'm not sure where your fishing, but other than the rare occasion and with dries have I yet to see a trout come up through a water column to eat a nymph. Trout pretty much exclusively feed left to right, and rarely up and down. IF you cant get it down to roughly the depth they aren't going to see it.
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