Subcubensis are not more potent than Cubensis:
http://www.shroomery.org/9644/Psilocybe-subcubensis
Cubensis v. Matias Romero are apparently often short and stocky (though not necessarily!), or otherwise perhaps Penis Envy if the caps tend not to spread out or not far, or
maybe Red Spore.
@second question:
As with cannabis it's both, but growing conditions are relatively more important and the choice of the substrain has a less consistent result. There has to be the right nutrients in the substrate so that the metabolism works properly. I'm not sure if there is consensus in the scientific community that psilocybin is an insect deterrent like natural cannabinoids, but I imagine that the mushrooms make the best of what they have. There are enzymes synthesized that are involved with the alkaloid pathway, recall the German research on adding tryptamines to the substrate. I wonder if supplementing the substrate with L-tryptophan works. Of course there is a ceiling.
About strains, I still think that the differences between Cubensis substrains are exaggerated. Genetics are definitely an important factor regarding the potential for certain properties like number of fruits, size, number of aborts, if they are short and stocky, tendency for caps to spread wide or keeping bulbous for longer and also alkaloid content. But, although some potency may vary between substrains I think there is more variance within the substrains.
A couple of things besides supplementing your substrate that should help boost potency are casing, providing all the nutrients (like a pinch of calcium sulphate / gypsum for example), keeping a close eye on all cultivation parameters like temperature and humidity and switching to poo as a substrate should also be successful.
But every substrain has it's limits. If they produce more fruitbodies the size will be smaller or the amount of flushes will be. Fast growing mushrooms just tend to absorb more water which is not going to do you much good. (but it's not usually bad either).
I don't really know if there is a downside to fast colonizers. It may be possible that mycelium that rushes to be strong and abundant spends relatively more energy and nutrients in that phase and it may come at the cost of the fruiting bodies. I'm not really sure. AFAIK, South-American and other tropical (as opposed to subtropical) substrains tend to have this trait but I never heard about them being lame fruiters in the end. It would make sense though, if you get fewer flushes from them relative to other types.
Another thing is that not every substrain is the same even though they may be sold under the same name. Once they are named there is a common ancestor so to speak, like specimen that are found in certain parts in the world and being called after the country, or after the discoverer, etc. After that they are propagated and each go their own way. The ones that are cultivated with general breeding selection (printing the beautiful ones but not the lame fruits) or better yet using petri-dishes and mycelium morphology selection get maxed out to their best potential over time while those that are just randomly propagated are only selected by natural selection, the survival of the fastest germinating spores.
I think that with well-selected ones you can still plunge back because if you use normal multi-spore propagation it is just a genetic crapshoot. As long as you do that there will be random variables and the result will remain somewhat unpredictable and inconsistent.
If you want very potent cubensis mushrooms maybe your best choice is PESA, they tried hard to make a potent substrain and apparently they have good potential. But if you grow them amateuristically they just probably won't reach that potential so there are no guarantees I'm afraid.
If there were a magic solution to all of this, it probably would not be a secret now would it?
Instead, check the shroomery and how they emphasize on all the different factors that together contribute to a solid product, together with adding more and more advanced techniques as you go along. That's the only way to really get better at it and achieve success.
I know people prefer the sight of a proper mushroom when they eat them or buy them from their source, but I would personally get an electric coffee grinder somewhere, and as you get a stash of mushrooms during your grows I would save them up and when you get a good amount, grind them all together. That way you homogenize your batch. IMO what is more important than trying to get the most potent mushrooms with the least amount of effort is to be able to know what to expect of your batch. With homogenization your trips may still vary but it should not catch you off guard with super weak and super strong mushroom specimen among them. Once you test your batch you can adjust your dose accordingly. Yes, you will have mushroom dust instead of whole shrooms but seems like the smart thing to do to me.
The fact that there are sometimes super weak and super strong mushrooms by the way, comes from the multi-spore thing. Using a normal spore print or syringe will yield mushrooms that are all genetically different. Some can be mutants, some big, some small, etc. If you would use a procedure to get a monoculture you effectively get clones that are much more alike (though still, like human twins there are still differences).
![:\](https://bluelight.org/xf/BL_Images/Orig_Emoji/wrygrin.gif "wry grin :\")
