I voted Silver here.
Silver went easy on Gray in Tartaros, so we know that his full power must have been beyond what we ever saw of him.
Kyouka also mentioned that Silver had demon form, so that's another indication that he had some sort of Transformation he didn't use against Gray.
But ultimately, what decided the match for me is that Silver is a Ice Devil Slayer and Invel is a regular Ice Mage. If Silver knows how to utilize his magic properly (and assuming there is no plot involved like in Gray vs. Invel), then Silver should be able to eat Invel's ice no problem.
Which not only give Silver a lot more power, but it renders Invel's attacks useless.
For me, Silver takes the win no less than high diff.