What you forget is when your margins are in the over the mid 30's you can afford to sacrifice some margins, when your margins are in the mid 20's you don't have so much room. So, with a slower process and a larger die the wiggle room is going to be much less for this particular part if they are aiming to make any money from it. Low-k is likely to to have a premium and may have some yeild concerns, but if it is the case that the die is smaller then that will alleviate some of that and a low-k (with a smaller die) should allow for wiggle in the clocks if the part has been designed for it.