I have the impression that you have very different questions here.
To answer your first question:
is there any research on the impact of font on readability?
Yes there is. You must first understand that the types / fonts are judged according to their "readability" (ease of reading words, sentences and paragraphs by an average reader) and their "readability" (ease of distinction of forms of letter). .
Studies have shown that readability tends to increase when using a "normal" or "regular" font weight (ie 400). Indeed, when words and phrases are able to read quickly, the reader's eyes slow down their normal blink rate, allowing the user to not tire of reading for long periods of time. Yet, when lighter or heavier weights are used in large blocks of text, readers tend to blink further because they have to focus more when they read. Lighter type weights introduce more negative space and heavier type weights introduce more positive space. Both ask readers to focus more.
For titles, your goal should be readability, but also readability. Studies have shown that fonts with higher x heights are more readable.
To answer your second question:
So here's the violin I'm working on http://jsfiddle.net/T7b6E/
Personally, I prefer the title with a cast-weight: 100 (smoother, modern, etc.)
The first thing to remember is that just by using
font-weight: 100; in HTML does not really create a lighter character. The weight must be in the font. Most standard fonts exist in 2 fats (4 styles): Normal, Italic, Bold and Bold Italic. In HTML this is
font-weight: 400 and
font-weight: 700. If the font to which you are trying to apply a different font thickness does not have this thickness, the browser will try to give you a rough idea of what it's could look like. And that could be wrong. And depending on the operating systems and even the browsers, this could be very different.
There are so many excellent web type foundry services on the market that provide multiple weight types, I would like to study that.
The general rule that I use with the type weights is: the bigger the type and the shorter the size (ie the titles), the easier it is to use lighter weights . The longer and shorter the type, it is better to use normal weights and heavier weights. This approach also corresponds to studies that show that people do not read, they scan copies online.