Firstly, I dont consider different patter to be a variation, unless it changes what the spec sees happenning in the effect.
As far as my patter goes, I dont even know what the buck's original patter is. Mine is probably quite similar, but I dont know.
I've never had a problem with people not seeing the effect though...that said, here's my basic patter:
*talk about deja vu*
Have them call stop, do the turn over
"So you stopped at a card. In this case, the card isn't terribly important, but rather where it is..."*do production* "in the case, between the two black aces, is your card, the XYZ. We'll take your card, sandwhiched between the....black aces? Was it?"
This forces them to associate their card, XYZ with the black aces, and you let them finish your sentence and tell you it was the black aces.
Now have them select the other card
"The ZYX...And just like the last one, it doesnt really matter what the card is...but where it is" *do change* "Between the two black aces...*PAUSE*...is your first card, the XYZ."
Let the effect sink it, pause here as well. let them realize what happened. When you see them look to the other aces, continue
"Now if that really did just happen, then down here...between then two red aces...we must have your second card...the ZYX"
Say "The ZYX" as you show them that card.
So there's my patter, I've never had anyone miss the effect, in fact, they tend to really like it...there you go!