well certainly trial and error for each individual is always a great way to go. i will just mention a few things briefly, as you touched on a few interesting topics related to exercise physiology, in which I am currently pursuing a master's degree.
in terms of recruiting muscle fibers, it always happens exactly the same way: every muscle fiber in a given muscle has a "ranking" based on the size of the motor neuron that innervates it. basically the smaller the neuron, the earlier the fiber is recruited. however, no matter what you are doing, the fibers of a given muscle are ALWAYS recruited sequentially, in EXACTLY the same order (starting with the slowest-twitch fibers, and moving on to faster and faster twitch fibers as needed). if the muscle only needs to produce a little force, it will only recruit, just as an example, fibers 1-100. if it needs to generate more force, it will recruit 1-500. if it needs maximal force, it will recruit fibers 1-whatever (except you will never recruit more than about 70% of the fibers in your muscle, except during extreme cases of adrenaline-induced fiber recruitment). so basically, there is no such thing as recruiting "different" fibers. you can only recruit "more" fibers. and that is done by subjecting the muscle to greater and greater force demands.
having said that, if you are so fatigued during your last set that you can barely get the ten reps, then yes, you are placing a demand on the muscle that will force it to attempt to recruit more fibers. however, the level of hypertrophy you will be inducing in those fibers is minimal, as the the average tension on each of those fibers is minimal. hypertrophy in a mucle fiber is directly related to the amount of tension you put on that fiber. so no matter how tired you get with 135 lbs, it is simply not going to put much tension on the fibers.
having said all this, lots of people make gains using different methods, so who knows... best of luck, though.
