Yes biotech has outperformed the S&P for years now, and yes some stocks in the group may be stretched. I also respect the market enough not to wax Pollyannish here. There will speed bumps along the way, but this powerful trend is up and it shows no signs of slowing down.
Could $IBB pullback to to 280-290 and still end the year at 360? Absolutely, and in a way you should hope it happens so you can get better entries.