I have a similar spec'd machine (double the ram, but I think if you have 8GB that's already enough that it won't matter), and my minimum fps was greater than 60 in both Sonic 2, which at the very least seems to be the most common benchmark. Certainly nothing as demanding as Yoshi's Island (although that game had a Super FX chip that significantly raised requirements). Someone on Exodus' own forum is saying Super Skidmarks is the slowest game he's played so far, though I haven't had opportunity to try that one myself yet. I'd imagine the most demanding Genesis/MD game to be Virtua Racing, which has a special chip of its own, but I doubt it's emulated yet (correct me if I'm wrong?).