I think that the 30t cog will not work well on the older (7800/6600 and prior) short cage rear derailleurs that have a nominal 27t max cog. You can push them somewhat, especially if you tune the B screw, but 30t may be too far. It may differ depending on the frame's chain hanger and where it positions the derailleur.

If you have a 50/34 or 52/36 compact then those derailleurs definitely won't be able to handle the chain wrap. You can push it a bit past the specification but that's too far.

I use a 50/34 and 12-30 for extra difficult climbing races. I use a 7603 triple rear derailleur for it.