It's a very hard question to quantify with any certainty. Let's say for example that you have one product that you make a mark-up of 7% on, then another that you have a mark-up on of 55%.
The product with the higher margin could net you more money even with a much slower clearance rate than the other.
I would be using a sell through rate just to indicate a possible market personally. For example, something that had X listings with low sell through would be a concern, but that wouldn't stop me looking closer at the product in regards to margin and marketability. What I mean in regards to marketability is just because other's are selling a product that may not be doing so well, that doesn't mean they are marketing it correctly, and I've seen plenty of opportunities where tweaking the marketing of a product has increased a sell through rate.
A sell through rate is something that I would suggest concentrating on a lot more when you have a basic stock profile, and you are looking to start fine tunning. If you start out by adding the sell through rate to your overall equation right from the start, then you risk placing an emphasis on that rate alone, and that could well make you over look products with good margins where the sell through rate isn't of prime concern.