I don't think they'll lose by 4 either, but if they did, we'd be ahead of them on goal difference.
You're right that Spurs will go ahead of us if they win, but if Ipswich beat Spurs, it has the added benefit of putting Palace in the relegation spots for the international break.
Not for one...
Pretty sure we could actually stay in 4th, if Forest get a spanking by Newcastle and lose by 4, Spurs don't beat Ipswich and Chelsea/Arsenal don't draw.
I wouldn't be putting money on it, but it's possible.