The other thing to consider is what kind of research is it and what are you doing? I know some people were considered research assistants and all they did was clean test tubes and didn't do much beyond that. Also what the research entails is what will catch the eye of AdCom.
For instance I know a couple of people who applied to the same schools as I and we all had generally the same interviewers. We all had research in different areas. Now that decisions have been made, out of curiosity, we asked the head of AdCom for the school what made us distinct from one another.
One of the reasons they listed me was specifically my research. Whereas the other people were counting population levels of some animals or monitoring growth patterns (all very vaild research mind you) I was doing the most advanced genetic analysis anyone my school has done. I looked a kb of genetic code for hours and hours trying to figure out this evolutionary genetic insertion problem the main research was having.
It was like a really big complicated puzzle which made it kinda fun.
Anywho, the chick from AdCom said they liked my research more because it was a bit more intense in a rather groundbreaking field (my work in addition to my profs and others will eventually be published) and was, as she said, simply quite interesting.
Perhaps this has ended up being long winded, but those are two things you should consider. Yes, doing research will beef up your resume, but you have to weigh your options against that and doing well on the PCAT and your physics class.
