First, doing sets of 5 is not working at your max. Maxing out would be trying to go for a personal best for 1 rep every session. In addition to this point, StrongLifts, Starting Strength, and AFP are meant as novice linear programs. Once you are reaching the upper limits of the programming and you're unable to continue adding weight to the bar each session, you would move to an intermediate style program which will lower intensity or frequency to allow recovery (usually the latter), or will cycle intensity (a heavy day, medium day, and a light day are programmed). Wendler's 5/3/1 is a good example of an intermediate program, and is a very popular next step. Also Texas Method (Rip's favourite).
Starting Strength uses 3x5. Stronglifts has you start at 5x5, but you will eventually lower to 3x5, then 1x5. In reality, neither is really better or worse. Higher reps early on in SL will add volume and allow you to practice the movement (given you are doing them correctly), but the real reason these programs are successful is because adding weight each session is a good motivator to get back into the gym, and being consistent is what drives progress.
Unfortunately, it's difficult to find something that works perfectly for everyone. Everyone is different in work capacity, recovery ability, mobility, injuries, etc.. Trial and error is pretty big in this sport, but that takes experience. You could try to work with a coach who will monitor progress closely and devise a program specific for you -- they will do the analysis of your work and modify programming based on your results. That isn't accessible to everyone, so this is another reason why SL/SS/AFP were designed. They give a good base for inexperienced people to work with. They are simple, motivating, and effective enough across the spectrum. You will always get stronger running them, but it may not be the optimal rate of progress for every individual.
The number of reps you use in your set will have an effect on how you progress. Longer sets will allow your muscles to grow in volume, but aren't necessarily optimal for strength. You will get stronger if you're adding weight, however. Alternately, shorter sets will build more strength but less size. These are general 'rules.' Sets of 5 have been found to be a good balance between the two (really sets ranging between 4-6 reps). You can build size with short sets if you keep your rest times between very low -- it ends up having a similar effect on muscle development as longer sets.
3x5 at 95 kg is 1350 kg total volume, and 3x8 at 75 kg is 1800. That's only a difference of 350 kg, which isn't super significant but could add up over time. It may be more difficult to continually add weight on 3x8 though. I would probably recommend staying the course and continue to push. If you find recovery difficult or you are stalling, you can try to mix up the rep scheme for a month or two as a break, but 3x5 is likely good enough.