Gerald,
I too had the same question, I couldn't find research... About two months ago I found a very talented individual on this forum (thanks DR team) who I walked through my concept of creating an SRP to VDP conversion report which would allow me to A+b test and compare conversion while tweaking SRP layouts to focus on custom comments, payments, etc...
Long story short Jon Berna listened to my needs and created an SRP to VDP report from scratch. We are getting ready to launch our new layout part of which will really focus around custom comments. While we may not have research...we will have very strong data on what consumers care about and influences in their shopping habits while on our website.
Maybe there are companies or research out there on this but when Jon delivered this for my team it unlocked a key KPI for measuring the shopping experience. This should be a industry standard KPI for web vendors and dealers.
Thanks again Jon for finding away to make this happen!