Well i think all you guys are to damn paranoid IMO!!!
every muscle gets worn the hell out when you are emphasising another muscle! You cant get around it, you just have to deal with it! Tri's are your prime example! they get hit with just about any pushing movement! so again, dont worry about it, just dont do a thousand sets of a given muscle! If you usually do 12-15 sets, cut it down to 9 and you'll be fine! but that is just my .02
and debaser!
The problem with ONE "perfect" movement for a muscle, is it gets redundant fast! What is the biggest way to get unmotivated to work out you say? I'll tell you, and that is doing the same movement over and over again! Variety is the key...Slight incline bench might be the "Best" exercise for bench, but it like tuna, gets bland after awhile!!! but again that is just MO
Peace