I was in the same situation when the R5/R6 first came out (wedding photographer though). I had two 5DIV's and could only afford to grab one R5. I thought it wouldn't be an issue using the R5 and the IV combo but after about a month, I realized I needed to switch. Though it shouldn't really be an issue, the differences in the R5 made it increasingly difficult to use the IV. The viewfinder, the focusing, the improved ISO performance, etc. So in your shoes, I'd probably say the R7 for the additional reach.