I'd say it'll very much depend on where you're going. GI is one of the "big and broad" subspecialities, so standards are likely to be varied. Research is always nice, but good recommendations would also be liable to do the trick. I'd venture to guess it can pretty much depend on the PD. Obviously, if he's authored 225 articles and 18 book chapters he's likely to be looking for a research-heavy resume. But there's also ample routine in GI, so a LoR saying you've "got the eye" will prob. satisfy the PD who's looking at a heavy volume.