too many letters....?!!?!?

I have been lucky to have a number of mentors throughout medical school and as a result I have several very good letters of recommendation. I am now torn because I was told to never send more than 4 (which I did, but they are all from my home program).

But I have just completed an away rotation at a well known school and I have a new letter from a very well respected orthopedic surgeon who told me he was going to write me a letter (and that he wanted to do anything he could to get me in).

Basically I really want to send this letter. But will it be too much to send this additional letter (to schools that don't have a specific limit)?

Any advice? Any programs that would respond poorly to an extra letter? Thanks!

Most programs only accept letter submitted from ERAS (so i was told, anyway). Even if your new letter is written and sent out, it will take a couple of weeks for it to be scanned into the system (again, my personal experience -- one of my LOR's was received by the ERAS postoffice on 10/16 and was added to my file on 10/27). Most programs close application cycle on Nov 1st, so your letter may not even get to them, unless you convince the program coordinator to let you fax or email it in.
If you're trying to get that letter to programs like Lenox Hill, that has a deadline of Dec 8th, you can try to go through ERAS -- if one of your original letters was not downloaded by the program, you may be able to replace it with the new one. Check the ERAS FAQ section.