Every 8 methods knock out at least 1 cache line for you (on x64, at least). You're probably not calling 8 adjacent methods on the same exact type either, you're probably doing something with a larger blast radius. Which means sacrificing even more of caches. And this doesn't show up in the microbenchmarks people normally write because they vtables are hot in the cache.

So you're really banking on this not affecting your program. Which it doesn't, if you keep it in mind and do it sparingly. But if you start making everything virtual it should hit you vs. merely making everything noinline.