The MasterCard version you're talking about is actually called the QuicksilverOne... which is different from Quicksilver.
The most serious change is there is a $39 AF instead of No AF. You have charge over $2500 a year on this card JUST to break even!
As far as sign-up perks... The Visa version gives a bonus $100 after spending $500 over 3mo (compared to No bonus with the MC version) and instead of 0% APR until August 2014, it's only May 2014.
Unless you can get a real Quicksilver w/no AF... I wouldn't touch it.
I just spoke to Capital One and the offered me the Quicksilver. It seemed like a good deal to me, can't wait to get my new card.