I think the ENVY is actually the better performer of the two and if it is possible to replace it, you should insist on that option. If they cannot get another, and they are willing to refund the price difference, I don't think you'll be disappointed with the performance of the dv6. I think you may be able to use the lessor ram and smaller hard drive as points of contention (although in real world application, only the 250GB storage loss would matter).