In 2002 I bought a pair of used 2400 Speedo black lines for $1,000. I believe they are 2403 B.... I have not used them too much in the last 10 years. They have 6 Outlets and three channels per pack, and there is a 1/3 stop dial down rheostat. I have a lot of 102 heads, and they have a couple of 202VF flash heads and I have five 103 heads which are a lot like the brown line M11, meaning they are convection cooled and use the same 150w quartz modeling lamp.
Back in the days of four by five sheet film and apertures like f / 45 the 2400 watt second pack was perfect. I like the ability to power 6 flash heads off of 1 pack, and that is something to consider. There is a 2400 pack that only has four Outlets and is popular with sports shooters.
The nice thing about Speedotron Black Line is how rugged it is, and the fact that they make flash tubes that can easily handle a 2400 Watt-second pop, and which have a really bright 250-Watt enclosed quartz modeling lamp, and if you need it you can also buy bi- tube and quad tube heads. Sometimes you just need a massive amount of flash power, and they have a head that you can use with two or even four 2400 Watt packs.