The equivalent to the SdKfz 251 was the SdKfz 11, rated at three tons. It would have been a STRETCH for sure. I don't know of any photos showing this combination. I think you'd have one burned out 251 drive train. Here's info I posted asking in reply about the similar weighted Pak 43/41.
The SdKfz 10 (1 tonner) hauled around light stuff like the iG18 75mm, Pak 36s or light flak guns. In a pinch it could haul 5cm or even the heavier Pak 40. (The Sdkfz 250 series shares this chassis)
Next came the SdKfz 11 (3 ton). The SdKfz 251 shares its chassis with the SdKfz 11, and not the SdKfz 7 (rated at 8 tons). The Sdkfz 11 (and sometimes the 251) were the vehicles tasked to haul the Pak 40 75mm , Pak 39 5cm, leFH18 10.5cm and sIG 33, 37mm Flak guns and nebelwerfers.
Then the SdKfz 6 (5 ton) was developed intended to haul the leFH18 10.5cm.
The SdKfz 7 (8 tons) was developed to haul the 8.8cm Flak guns (Flak 18, Flak 36, Flak 37, Flak 41). Other weapons like the Pak 43, Pak 43/41, sFH18 15cm howitzer and other weapons in this weight class were hauled by this, the "Krauss Maffai" Sdkfz 7.
The SWS can be placed next. A relative late comer, its capacities were similar to the Sdkfz 7, along with its loads.
Next was the SdKfz 8 (12 tons). It could haul all the weapons listed for the SdKfz 7 as well as some heavier pieces.
Finally, the SdKfz 9, commonly referred to as the "FAMO" was rated to haul 18 tons plus. It was developed as a tank hauler with the duty as a heavy artillery prime mover a very very low priority. It was used a TINY bit to move 24cm morsers. (There weren't many of them BTW)
To answer the original question, the SdKfz 7 and SdKfz 8 and SWS were the prime candidates for the Pak 43/41. The FAMO would be overkill, and the others would be at a severe overrating to haul the Pak 43/41.
