One thing is certain, if Ferdinand remains on the Habsburg thrones (so he remains the King of Hungary as well), then the reforms of 1848 would still be in use in Hungary, the Austro-Hungarian war of 1848-'49 wouldn't occur. With a civic country in PU with Austria though, I don't think the maintaining of Metternich era is possible, he have to fall, and most probably a similar system to OTL 1867 Austria would be established.
Let's roll with this idea, a more "civic" establishment both in Austria and Hungary would lead to an earlier, faster and more effective modernisation of the two. Now, let's see foreign policy. Austria and Hungary would most probably be involved in the Crimean War, since the Habsburgs doesn't owe the Tsar like in OTL. What could the Habsburg earn from it? They could eradicate the Russian influence on the Balkans and most probably could attach Wallachia and Moldavia (,which at this point regains Bessarabia) to their own sphere of influence. Also they could be the power, which leads the liberation of Balkans from Turkish control, which could earn them significant prestige amount the Balkan nations and could draw them towards their sphere of influence.
A more modern Austria and Hungary might not lose the war against the French and Piemont, but still would lose the war against Prussia in my opinion.