For comparison, I'm running 295/35/19's on a 10.5 in the rear. (fronts are 275/35/19 on a 9.5in wheel)
I like the twisty's as much as the straight line so I opted for 295 over a 305.
I have not been disappointed with straight line traction in the least. They grip and go.
When I bought those wheels, I spent some time doing research trying to figure out what size tires to put on them.
You can follow that journey here: 19x9.5 and 19x10.5 - Tire Options?
and learn a lot in the process!
Essentially you will learn how to find the information you need from tirerack in regards to tire sizes, and use that in conjunction with a wheel/diameter calculator to find your optimal size.
2014 Mustang GT Premium (deep impact blue)
Too many mods to fit in my sig.
Follow my build list on my blog
. (still updating mods installed so far)