I can see the point in going from say 256 to 280 but 8mm is nothing and I dont think you will notice any difference unless it is cheap / free.
8mm larger is nothing...
But they are 5mm thicker (I seem to recall...25mm vs 20mm) and hence have a much higher thermal capacity...so they won't overheat and fade as fast.
Make sure the 288mm set up you get is the Mk3 288 set up, not the A3/Mk4 set up...as the offset is different.
They both fit, the Mk3 stuff goes straight on, whilst the Mk4/A3 stuff needs a 6mm spacer behind the calliper carrier to space them inwards to line up with the later offset disc....which means you also need 6mm longer high tensile longer bolts to bolt the carriers to the hubs.
If you are going later style 288s, just go the whole hog and fit 312s - if your wheels will cover them.