i know what you mean about the stresses of LoRs.. I worked with my professor in his lab and saw him every day. We had a great relationship but he totally screwed me on my letter - he really liked me (at least i hope he did) but he sent it in soooo late.
I did not expect a problem with my letter from him but he totally ruined my first time applying. - obviously had i known he would be so nonchalant and unconcerned wiht my pursuit into dentistry i would have had someone else write it.
you never know with college professors, so in my case, he decreased my chances.