Progressive overload: more thoughts (effort)

I was thinking more about the intensity and effort and their effect on muscle growth. I do tend to agree with Doug McGuff (Body By Science) - it's more about Time Under Load than anything that defines the impact in terms of level of stress (stimulus) applied to the muscle. Plus of course load itself (resistance). Other parameters (speed, number of reps, type of resistance) seem to be of less importance. Another thing I was pondering upon is what they call level of Perceived Effort. Despite the fact that it may be deemed as somewhat subjective by some people I believe that when used properly it can be a powerful measure of workout efficiency.

I use a simple system based on a few concepts I found in Stuart McRobert's Beyond Brawn to measure my effort on a set. Here's how it goes: I estimate the effort on a scale 1 to 10 like this -

10 - all-out effort, to absolute and unconditional flat-out failure (I only use positive part of the movement), the final rep cannot be completed no matter how hard you try without messing up the form;
9 - very tough effort; the final rep is completed but one more full rep would be impossible (again, with the correct form);
8 - hard effort; I completed all the planned reps with good form and could probably do one or maybe even two more if my life depended on it. But that would be it.
7 - solid effort; The weight is heavy enough but you could probably do 3-4 more if you were to go all-out.

I don't usually do anything below 7.

Here's why I like this system no matter how subjective it may appear. It allows me to keep track of my effort and intensity which adds one more dimension to help me measure the efficiency of my workouts besides weight alone. Let's say for my lat pulldown I increased poundage by 5 lbs and attempted the same 12 reps that I did last time with smaller weight. I want to make sure that I not only complete my target 12 reps but also do it with the same form, speed and effort! Let's say I did it with PE (perceived effort) of 8 (had a couple more reps left in me) last time but this time the weight felt very heavy and I ground out that final rep with extreme effort and strain and after much huffing and puffing decided that it was an honest 9, almost 10 then - no matter what the weight is - I may have not been as successful as last time. It could either be too much of an increase in resistance or my recovery has been insufficient for some reason (either too short or otherwise compromised).

One other thing. I've read a lot of discussions in bodybuilding community on whether or not training to failure is "the way to go". There's a variety of opinions and from what I read it's not a clear cut solution. My feeling is that although going to failure does indeed exemplify an all-out balls-to-the-wall effort when it comes to training intensity but it appears that it may also be too much of a burden on the CNS. Seems like its taxing into our body's recovery capability could be way too severe - to an extent where its negative side outweigh its benefits - for an average trainee, anyway. I feel that going to 8 or 9 (vs 10) might represent a "less is more" approach still providing enough stimuli for the body to grow without overtaxing it. I found for myself that when I was taking almost every working set to failure I would be tired and low of energy pretty much all the time.