Do steroids matter ?

Depends on your goals. If you want to compete, wether it will be powerlifting or weightlifting or bodybuilding competitions, you pretty much don't have the choice. but to the average joe that want to improve his physique, his muscle mass ratio, his strength, he certainly don't need steroids to do it.

how bad can you become naturally ? how much muscle mass can you hope to gain naturally?
-different studies tend to converge saying you can gain about 25-50 pounds of muscle mass, depending on your age, size, muscular developpement... we cannot say for sure there is a formula but you can hope to achieve an good muscular and lean physique, wihtout any steroids. what you cannot hope is, an extremely muscular, lean physique, that will win competitions whithout any form of steroids.

Irongangsta.com seems to desillusioned to even believe you can reach more than the physique of a gymnast, but he doesn't seems to understand the way the body build muscle completely neither.
there is no reason why a gymnast who doesn't give a shit about muscle mass would become the most possible muscular physique that you can obtain naturally, just because he is an olympic athlete. Sure, gymnastic do increase your muscle mass, but not to the point it will make your reach your muscular potential. why ? because such gymnast never use the overload principle, the just use their own body as a weight. and since the weigth never increase, muscle do not either.

One can argue that leverages in gymnastic gets pretty hardcore, and replace the overload principle because such leverage becomes so hard that it is comparable to an extreme weigth, but studies have shown that this is not the case. Gymnasts, though they have often some really good strentgh, cannot really hope to deadlift or bench press a lot without a prior training in those. they often wont do bad, (of course) they are athletes after all, but they dont compare to powerlifters (even naturals ones).

The main reason behind this is the fact that muscle tend to grow thicker with more weight,, wether the leverages becomes harder or not. Also, bodybuilders have a very special way of increasing muscle mass that no other sport ever does, wich require one to train to failure or close to it, repeating the exercise movement with an approximal maximal weight of 60-80%. Only in bodybuilding you can find exercises that can meet theses requirements.