In Chicago, we actually ran an entire local tourney as 3/5, recently. Frankly, it adds more time than you think. If I had to estimate, I's say it increased the amount of time by 50-75%. So, if your tourney would've taken 2 hours, it'll take 3-4 hours as a 3/5 event.
That's... literally the math.
Like, FT2 means sets last 2-3 games. FT3 means sets last 3-5 games. It's a baseline 50% increase in tournament length, although the variance is such that anytime somebody comes back from a 0-2 set (Which is the entire point of 3/5, right? That's one of the two precise reasons to switch to 3/5, the other being coming back from 1-2 sets) the length of the set increases by 150%. Holy shit! A 2-hour tournament extends by
a minimum of an hour, and a maximum of 3 extra hours. Not saying that's likely; just saying that's a potentiality.
As a TO, my question for you is, "Are you asking to play more games, or are you asking for
the top players to win more often?" In the former case, you can just play casuals. In the latter case, we encounter a specific problem that is highlighted best by the difference between Japanese and US tournaments-- tournament volatility. You see, we can do every set 3/5 and even do triple or quadruple elimination (or even round-robin!) but on the macro scale all that does is make the best players more apparent. The point of 2/3 and double elimination is to allow room for good players to make mistakes and also allow bad players a longer chance to enjoy the experience (which are good things
in moderation), but we do so at the cost of time and drama. It might not matter much to you personally now, but if you are a player who could potentially place (or even win) then it absolutely matters to you and the audience that you be given that chance. While I'm not expecting Sonicfox to get randomed out anytime soon, it's asking a lot less for somebody to take 2 rounds off of him than 3, and that matters for the overall environment. In Japan, they play Single Elimination, which means they have a greater variety of winners. Japanese players
love coming to the US for tournaments because they view it as much easier for them to win (and they're right). Conversely, there's something to be said for different people placing at tournaments, both us as a community and to outsiders who need to see a good, inviting impression of our community.
Another thing I need to ask you, and by "you" I mean the parts of our community that want longer sets, is "How consistently do blowouts happen?" I had a debate a few years back with Melee players because I believed that switching to 2-stock (or even 1-stock!) would not affect tournament results at all based off the streamed top 8 at Evo that had just occurred at the time. 4-stock as a rule only exists to arbitrarily extend the length of the game, boring spectators who are not invested in Melee, without actually contributing mathematically to results. Whoever took the first stock went on to win 85% of matches with the exception of Wobbles, who was only excepted because he could remove a stock with a single touch at any point. If you changed the game to 2-stock,
nothing would be affected other than sets not lasting 20 minutes each. If you want SG2E to switch to 3/5, are you sure it will make a difference?
As
@keninblack said, top 8 being 3/5 in a 64+ sized tournament is fine, but anything less results in a huge increase in tournament length for little potential gain.