M109 is normally a manual loading gun. Any howitzer with an autoloader can fire fast. For example, the Bofors FH77BW L52 Archer SP 155mm system has a autoloader, and it has the ability to fire in salvo mode, which is 3 rounds in 15 seconds. It also has the ability to fire off its entire magazine (20 rounds) in 2.5 minutes. Comparing a system with an autoloader to a system that is manually loaded in the same size catergory is comparing apples to oranges.
And as I said before; it is not the length of the barrel that affects the range (it does, but not by much), it is the design of the entire system (breech, tube, etc) that gives it the extra range. The main issue with most of the 155mm systems is the way the gun is rifled; the shell rides on raised "lands", and uses a soft, metal driving band on the shell to spin the shell. The ERFB system takes a completely different approach, as the design uses "reversed rifling", grooves cut into the barrel. The shell rides the rifling via small "fins", and had no soft-metal area where the propellant could "blow by" the shell, allowing much more powerful propellants to be used. The resulting ERFB ammunition is key to G5's and other ERFB designs, as the shell is now a "pointy" looking shell that carried more explosive than conventional designs, had much lower drag at supersonic speeds, and was more accurate. Due to the fact that more powerful propellant is used, and the improved accuracy of the rifling, when using "zone 11" propellants (as opposed to maximum "zone 7" for the M109), the GC-45 (the gun that the G5 was based off of) could place base-bled rounds at 39,000 m with the same accuracy as the M109 at its maximum range of 18,200 m. At shorter ranges the GC-45 could easily repeatedly place rounds into 10 m circles, and could be used in the direct fire role to about 3,000 m.
The design has been demostrated to be a headache and a serious thorn in the side of anyone who is at the wrong end of the system. When the G5 first saw service with the South Africans in 1982, the gun as put against Cuban and FRELIMO forces in the Angolan conflict, where they soon completely wiped out FRELIMO artillery in the border areas. With highly accurate and long range artillery pouring down far behind the front lines, any offensive actions by the FRELIMO and Cuban forces were impossible, and led directly to the ending of active hostilities.
The G5 (in the version of the GHN-45) was also sold to Iraq, who had been on the wrong end of artillery exchanges during the early days of the Iran-Iraq War, and wanted a new weapon that would completely outrange the older U.S. 155mm designs in Iranian service. They had the same effect that the South Africans saw in Angola; they stopped the Iranians from being able to conduct offensive movements whenever a battery of GHN-45's were nearby. The GHN-45 was a serious worry for Allied commanders in the first Gulf War, as almost the entire U.S. Marines air corps had to be dedicated to wiping them out or supressing them.
Most nations are starting to move towards the G5 or guns that use the EFRB formula. Systems using the EFRB formula in the L52 length are becoming the de-facto standard in 155mm artillery, and even the Chinese now are slowly adopting a version, albeit in the L45 caliber; the Chinese apparently will adopt the NORINCO PLZ05 155mm SP system, and they have already adopted the NORINCO PLL01 155mm towed system, of which 54 howitzers have been adopted that are known, and have been issued to an independent artillery division in Beijing Military Region. During the military parade in Beijing on 1 October 1999, this division demonstrated the howitzer to the public.
If Denel decides to put an autoloader on their G5-52, the G5-52 will match the M109A6 Paladin's autoloader fire rate. In fact, Denel has two systems using the G5 on a autoloader; one is currently available (the G6 SP 155mm system) and the other is the T5/T5-2000 system. Both can do 8 rounds a minute. The G6 is a 46 ton system, so I doubt that the CF will ever express interest in it, but the T5-2000 will probally be of some interest, as it is a truck mounted system, a-la Bofors FH77BW Archer or GIAT CAESAR.
Also, using the Excalibur round in the G5 or Bofors gun will result in the range being increased even further; 60km.