My opinion is that the tempo isn't as important as some may think. The slower the tempo, the less reps you can get (or the less weight you can use). The opposite is also true (naturally). Eventually, the total TUL is about the same either way, unless you use less weight in order to emphasize TUL (not recommended).
Some time ago I experimented with a HIT-type program, which advised 8-12 reps and a 2/4 tempo for each rep. Not much difference really. You could get a good burn of course, but that's it. And the weight of course was much lower than my "natural" 8RM.
So, after spending much time thinking about this, I've come to the conclusion that you should do your reps as slow as needed so as not to hurt yourself. As long as you are injury free, you are fine. Just keep incrementing and do not worry too much about this.