275/40 square on 9/10 staggered wheels?

[clutchkick]

So I have 20x9 and 20x10 staggered wheels and I am starting the hunt for new tires. Currently have 275&315 tires but I autocross and am considering 275/40r20 square for a more balanced setup and get rid of the insane bulge in the rear. My question is does that even make sense? Will a 275 even be enough grip, because oversteer out of corners can be an issue even with the 315s I currently have (they are a 3 year old all seasons though so not ideal). My other option would be getting a 275/40 305/35 setup to slightly lessen the width difference as I save up for new wheels.