To send or not to send? (4th LOR)

There is a lot of knowledge on this site so here is something I've been struggling with. I am applying to IM and feel confident I have 3 strong LOR from attendings that know me well (1 research, 1 chair, 1 clinical). However, I'm not sure about the 4th clinical since I just didn't get to work with this attending as long. I did ask the whole "will you write me a stong LOR?" and they accepted but I'm just worried it will pale in comparison to the other presumably outstanding letters. When there is doubt about the quality of the 4th letter, is it better to just send 3? I figure most LOR will be generically good so I don't know if having that sort of add'l letter will add anything. On the other hand, I don't want to be at a disadvantage by not sending, particularly at very competitive places where I'm sure most ppl will be sending 4 LOR. Very confused here... Thanks in advance for the help.