I went back and pulled some timetables for comparison. First, we have the Olympian Hiawatha and the Afternoon Hiawatha, and their times from Chicago to Minneapolis:
1956
No. 15/16 Olympian Hiawatha
Dep. CHI 1500
Arr. MSP 2145
Time: 6:45
Dep. MSP 0635
Arr. CHI 1345
Time: 7:10
No. 2/3 Afternoon Hiawatha
Dep. CHI 1300
Arr. MSP 1945
Time: 6:45
Dep. MSP 1230
Arr. CHI 1915
Time: 6:45
There's what seems to be about 25 minutes of pad for the train EB vs. WB, though that may also be some quirky operational delay (or more stops...let's not forget that a lot of stops were served by interesting mixes of trains).
Next, we have A-Day, with the May 1, 1971 Amtrak timetable:
1971
No. 31/32 Empire Builder
Dep. CHI 1045
Arr. MSP 1840
Time: 7:55
Dep. MSP 0710
Arr. CHI 1505
Time: 7:55
As you can tell, over an hour has been dropped vs. the Afternoon Hiawathas, and roughly an hour vs. the Olympian Hiawatha.
Finally, today from the Summer/Fall 2013 timetable:
2013
Dep. CHI 1415
Arr. MSP 2231
Time: 8:16
Dep. MSP 0750
Arr. CHI 1555
Time: 8:05
Another 10-20 minutes have been added...not nearly as bad as 1956-71, but still going the wrong way. It's also worth noting that the 30-minute pad at MSP on A-Day has gone to 44 min. WB and 45 min. EB.
This example is illustrative of a point worth noting: The times in the 1950s may not be anything special in some respects, but there are more than a few cases where I think some of us would give our right arm to have those speeds back.
Edit: Please note, moving the terminus from Minneapolis to St. Paul drops about 30 minutes from the trip in 1956 (so you get 6:15 each way). I mention this because of the impending move to SPUD...and it suggests that six-hour runs between Chicago and the Twin Cities wouldn't be entirely unreasonable to hope for as part of such a project. This may not be a silver bullet, but considering what the Builder does with its current situation I'd be hard-pressed to see such a service
not succeed.