I am guessing when 'The Speed of Light' phrase is used for calculations its usually taken as the constant speed of light through a vacume. Which is constant (first line of wiki's entry on speed of light). But yea, it does speed down, even depending on the substance its going through, such as how the bending effect works in water.
But goign back to your original question, your going to hve to make up your own scale anyway. Even if you use real distances and the exact warp scale would still leave several days/weeks of traveling at a high warp between solor systems. Which is taken out of the show (you can work it out how long its been by the stardate given....if your that geeky)
The Enterprise D usualy cruises around at warp 7 if i rmember the sow rightly, which is a day for each lightyear. The nearest star to use is 4.2 lightyears, or at warp 7, around 4.5 days. which is about 4.5 days too long for anything a person wants to sit through :)
But goign back to your original question, your going to hve to make up your own scale anyway. Even if you use real distances and the exact warp scale would still leave several days/weeks of traveling at a high warp between solor systems. Which is taken out of the show (you can work it out how long its been by the stardate given....if your that geeky)
The Enterprise D usualy cruises around at warp 7 if i rmember the sow rightly, which is a day for each lightyear. The nearest star to use is 4.2 lightyears, or at warp 7, around 4.5 days. which is about 4.5 days too long for anything a person wants to sit through :)