Ok I'm usually good with this stuff but I'm starting to fail. I have a few questions.
1. What size adapter covers the stud completely without having to cut it off. ( I have two sets of 5x105 now but want to do some thing ridiculous)
2. On a 16x7 what dose the offset or back spacing need to be to be close to flush with space from answer to question 1.
Thanks guys. I have had this idea since I bought the car and I plan to go for it if its not going to cost me millions.
1. 25mm
As mentioned in the original post, check your mounting pad. If you have the crater thingies, you won't have to worry about cutting the studs regardless of adapter size.
2. It depends on the tires you have, and your definition of "flush."

Have you tried playing with the little tool I posted in the original post?

I'd recommend checking that out as well if you haven't already done so.
I want to say et +20 to +30 because 17x8 +30 (with 205/45) is very flush, and +18 is the 7" equivalent in terms of poke but as I said, depends on the tire. (higher offset to fit meatier tire)
In my opinion, your car already looks pretty awesome as it sits right now. (seems fairly flush as well; you could just use those specs and convert)
Thinking about changing things up already?
How about wobble bolts? Can't you fit the euro-Ford/Volvo 5x108 w/ these? I know going 5x100 would be pushing it.
The Sonic has studs and lug nuts, so I think you would be looking at wobble nuts rather than wobble bolts. (unless you want to convert it, but that would be more of a hassle than it's worth)
That being said, you might be able to do it. Maybe contact MPFab since he has them on his car right now.
http://www.sonicownersforum.com/forum/wheel-tire-discussion/7024-go-big-go-home-7.html#post165868
Here are some updated pics.
In order to keep from having to open the wheels up around the lugs, I opted to redrill to 103x5 and make some varience nuts to make up the difference. You can also see the hubcentric ring my machinist made for me as well.
Redrilled wheel
Closeup of redrilled wheels. You can see how much the tapered seat is shifted over
Bolted in place. Without really looking at this, most would not notice the lug nuts are off center in the wheel.
Hope that helps.
