The thing about having supply vs going in quicker is that there is usually a low-level AI planet next door with defenses running in the tens of ships. If your lucky, you can catch that planet, nix the command station, and use mk2 engineers to conjure up a impromptu fort.
From there, merely spam turrets until you are happy, and send your fleet next door as fast as possible.
This especially goes for core planets imo - i could not imagine taking down a core planet without supply. So much of my attacks rely on the ability to pull damaged ships out of the fray and repair them... Granted doesnt always happen when we are talking core planets.. but on core planets, I tend to also have an entire fleet yard as far away from the gravity well as possible. This allows me to replenish lost ships /on the spot/ (as well as drawing away hostile ships now and again).. Actually, this is probably more perma-mine related, as its a pony to get anything across perma-mines.