Certainly it would improve the handling with the 305's on the rear. The principle behind that is the more/wider contact with road makes you more stable on the curve. I do recommend have your camber at -2 at the rear.
It does make your tire wear uneven though but it is what it is...you could not get both worlds in life either.
The down side you sacrifice acceleration as you spin a heavier mass with the 305.
I don't care as you said you don't race the car in the track and dd it on the mountains the 305 is just perfect! I love mine!
