Fat content in chocolate chips Recently I got a bag of dark chocolate chips, 12oz (340g) for $3.95.

(15g per serving) It's total fat content is 4g, 2g of which being saturated. The bag does not state the cocoa content percentage.

(40g per serving) In comparison to another bag of chocolate chips of the same brand labelled as semi-sweet. It has 14g of total fat and 8g of which is saturated fat. However, this pack cost $6.20

My question is, does the fat content affect the 'meltability' of the chocolate when used in chocolate chip cookies? I'm aiming for a cookie that is filled with gooey chocolate rather than firm chocolate chips around. Should I get the semi-sweet pack instead?
The second pack is a very slightly higher fat content, but as chocolate is cocoa solids+cocoa butter+sugar, we still can't be sure about the total cocoa content.

The melting point of cocoa butter isn't well defined, but two different dark chocolates will have a very similar melting point, so both will melt in baking, and solidify when the cookies cool.  

The solidifying behaviour of chocolate is interesting in that it cools to around body temperature while still liquid, than solidifies rather slowly, which is why it can seem cool but still be gooey in freshly baked cookies.

In the end, if you bake the cookies then serve them almost straight away, both will still be molten. If you let them cool fully, both will eventually solidify. In between, you can probably make more difference by serving them on a warm plate, or leaving them to cool in a warm kitchen rather than a cool living room.  The more expensive ones may end up nicer overall (on texture or flavour), but unless you want to arrange a blind taste test, there's no obvious reason to pay the extra.