I guess it depends on the venues you are playing. However, when evaluating your tone from a distance, you do need to get out in the room as far as possible. In a bar, that might only be 20 feet, but in theaters, etc., you need a VERY long cable to get anywhere. The reason being is that low end doesn't develop until you are out pretty far in the room and if the PA is handling bulk of the signal, you need to get far away enough from the stage to get out of the area of the stage bleed.
As far as the delay goes, let's round off the speed of sound to 1,000 ft/sec (It's actually around 1140 ft/sec depending on altitude, temp, barimetric pressure, etc). This means that by 30 feet out, you are dealing with a 30 ms. delay, which is where you would hear a discrete slap if you heard the signal right next to you and then off the stage. This is definitely more than enough to affect my timing with a drummer. In a decent size room, if you get 50 feet out, it gets really out of hand. OTOH, that's where you can actually start to hear the real tone of the bass out in the room.
Funny aside: I used to see Albert Collins a bunch. He had this 100' cable on a big reel that he would use with his assistant to get out into the room and at one show I saw at Jonathan Swift's in Harvard Sq., he went all the way out to the street and regaled passers-by. A few years later, he started getting more notoriety and I saw him at Great Woods (now the Tweeter Ctr. or some such nonsense), and the whole 100' reel barely got him to the side of the stage and halfway down the steps to the front row!
