Actually, Milwaukee alone is a lousy pick for 220 MPH: The distance is too short to derive much improvement over 150 MPH service (especially if you don't run the trip as a non-stop service), and even then I can't see much point in pushing the route beyond a 60-minute one-way trip (86 MPH average speed; depending on the alignments and so forth, a non-stop could probably manage this with a top speed in the 125 MPH range if there aren't too many slow-running slots between CHI and MKE). Cutting that to 45 minutes (115 MPH average speed) probably qualifies as showboating (we have a bullet train commuter line!), and absent some kind of expansion plans I would start raising the specter of wasteful operation speeds beyond that.
If this was in the context of something that went on to MSP, there might be a case for it...there, you get real benefits out of a faster train because of the distance involved (418 miles); that same 60-minute CHI-MKE run at 86 MPH cuts your travel time from 8:16 to 4:50, while an average speed in the 115 MPH range gets you around 3:30-3:40 (or, in other words, the improvement is 1:10-1:20 rather than :15). Likewise, if MKE-CHI was an extension of CHI-STL, I'd grant that it would make sense (even though I think the amount of through traffic would be...well, dubious at best).
I am wondering...would the bullet train between STL and CHI include some kind of convenient connection to downtown (and no, I don't count a basic Metra train) in the package? If not, my gut is saying this project has a real problem lurking in the wings.
Edit: Actually, MKE-CHI is something along the lines of RVR-ALX (ALX-WAS is, frankly, impractical to impossible to upgrade): Even assuming you could blast the alignment through, in a vacuum it makes no sense to run a train down that 101-mile segment too fast. Going off of the old Blue and Gray Clipper timetable (1:59 for a slightly longer route from 1956, terminating on Broad Street instead of on Staples Mill Road), you're timetabling around 55-56 MPH overall and about 60 MPH RVR-ALX. Right now, that section runs about 2:10 on the faster timetables (1:50 RVR-ALX).
To cut RVR-WAS to 90 minutes, you have to cut RVR-ALX to 70 minutes (86.5 MPH). 80 minutes would require 60 min. on the RVR-ALX section (101 MPH), etc...at some point, the project doesn't make sense in a vacuum. Of course, if you were doing this in the context of a WAS-CLT/WAS-ATL line, or as an extension of the Acela (should Amtrak become so possessed to think that a worthwhile investment on its own...yeah, right), this might make sense. Alone, though, it's a non-starter.