I might be able to help. I ran into this same question about a year ago putting together my Space Wolf army. I found the Onslaught ones to be a little small. Here's a pic where I "mounted" them on the shoulders of my Venerable Dread as pelts for a bit of size comparison:
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I ended up using Cobblestone Casting's wolves instead. They're 10mm so much bigger, but they're beautiful sculpts. General consensus was that they were more Thunderwolves than Fenrisian in size, but I thought these had more of a presence and looked like could actually attack something in 40k:
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Hope that helps!
