High specular settings are noise monsters/producers. On various pages I've read on Lux, all agree to get the best results, keep the spec under 84. Personally, I like 50 or under, except on skin, and that all depends on how glossy you want it to look. With other materials, you can also use the specular to give it a certain color tint in addition to the diffuse channel (aside from whatever the texture is). Where this comes into play more often is on non-uv mapped materials, where there is only geometry and the surface itself, like the test tube rack for example. Set your diffuse to whatever color you want, and glossy or matte, and try a specular around 15-45 and you'll do fine. If going metal, all you need to worry about is either a preset or the custom metal color (avoiding straight black or straight white) and your polish value. 

Do a test render with one material like this and from there you'll get the idea ;-) 

With a set that has so much glass, your specular settings need to be juuuust right to get a nice, clean render. Gloss can be pretty high without running into problems. 

Edit: Just for reference in this context, when I mention '84' or other numbers, that's for all three colors (red, green and blue). I use the color picker and the sliding bar to the right, then fine tune if I need to with individual colors. Example 55, 55, 55 or 21, 0, 0

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