Those stories of goonch which killed a cow is just ridiculous, you should not believe in anything you hear. A very large goonch may reach a weight of around 100kg, what would be more than most wels (but still nearly 50% under the recorded maxium weight of Silurus glanis), but thats still only much too small to pull a cow underwater. There is also no reason to think they can exceed their known maxium weights again fore about 200%.
In a hypothetical fight between a goonch and a wels you had to say at first which sizes you mean. Same weight, same length or largest ever recorded specimens? Given the fierce teeth of the goonch, I would suppose they could seriously injure even a same-sized wels, and their mouths are also not lesser wide (actually compared to the total length even wider).