Ferrari won't upgrade i hear until Spa/Monza as they have found that if they upgrade onto of the 30hp upgrade, they can add another 55hp to that figure. It may mean they have another 100hp for the end of the season, and building into 2016 they may build a nice little beast.
Mercedes are bringing an upgraded power unit i hear. All Mercedes powered cars will have an extra 30+ HP as all, barring HUL (ICE/TC/MGU-H/MGU-K/CE) & HAM (CE) are still on their first of any component part. This is ominous for the middle part of the season for the Mercedes powered drivers. It will bring Williams back into the hunt, be good timing for Lotus and Force India and possibly worry Toro Rosso/Red Bull/Renault.