RE: distinguishable, you'd need to think about why these facts are different from Williams v Roffey. For example, you may take the view that there isn't actually a practical benefit here. You'd need to think carefully about what practical benefits actually are.
RE: overruled, the decision in Foakes v Beer (essentially) is the rule in Re Pinnel's Case. Its arguable that it goes beyond part-payment of a debt and that Williams v Roffey is incompatible with it. O'Sullivan wrote an excellent article on this in the CLJ. I believe this idea may have been mooted in the High Court recently.