I've watched Vick a lot this year (twice vs my home team Panthers, twice versus the Buccs, tonight, and a couple other games).
1) you cant go by stats alone, he has intangibles that dont show up in the rushing yd or passing yd column.
2) at this point in his career, he/Falcons are over-rated as a quarterback/team. Thier defense is brilliant sometimes, but lately have been giving up 20+ points a game. They have no real standouts on defense, but when they work as a team, and if the matchup is right, they shine. Thier running game with Dunn, that train that's numbered 45, and Vick is often better than average, but sometimes they cant outrun thier O linemen.
3) Vick throws bullets, often his WRs cant hang on. He can work on this though and get some touch on the ball.
4) his presence on the field and highlight reels mean Defenses play against him differently. Lots use the QB spy method with a linebacker while pass rushing him hard. This worked great for Tampa Bay (a team who he's never had a big play on) but not every team has 2 Pro-Bowl D linemen to rush him and a Pro-Bowl linebacker to spy on him. You can see from the clip of tonight's game that Green Bay's spy couldn't make the play. This leaves you with 1 less guy in coverage as well so your other players have to step up.
If I had to put money on the next game, I'd say the Eagles. Donavan and Vick both have the ability to make plays on thier feet (depending on how good McNabb is). The Eagle's Defense will probably do better than GB's did, in rush D, pass D, interceptions and forcing and recovering fumbles. It wont surprise me if the Falcons win, but I think the Eagles have a better chance. In the end, it's all in the matchups. It depends on how the offenses and defenses and thier plans matchup.