Tire question

[Rez]

I am looking into getting Continental DWS to replace the stock tires but the front 275's are back ordered since May 2010 with no end in sight. I found 295/40/20's however and have been thinking about going square set up with 295's instead of rear 315's. This way the tire diameter is the same albeit slightly bigger in both ends. Any downside in doing this? I don't really see a need for 315 in rear since the car understeers quite a bit with that stager set up.