Not sure what criteria we are using for oversized. I usually base it on larger than the RWS or the Robin Wood (which I use often). Last night I did two readings for people, both starting with the Robin Wood which they had no problem shuffling.
Then I used each of baba-prague's decks (Tarot of Prague and Baroque Bohemian Cats) and they had a noticably tougher time shuffling them. So maybe they fall into this category as well (mind you, I love the size and feel of both these decks).
Dan