Currently the M109 does not have an L52 gun. It's still just an L39 - I expect the next generation will have an L52 and maybe an autoloader.
The M992 is my second choice after the K10. The M992 originally came with a small conveyor that stuck out of the ass end of the M992 to transfer ammo from vehicle to vehicle like this.
The troops hated it because of having to back the vehicle into place and most of them have been disassembled and the transfer is just done manually from one to the other. Which is fine on peacetime exercises but . . .
The K10 has its conveyor built into the front which makes it easier to drive up behind the K9 and extend the beam and continue to resupplie while under armour.