I don't think the difference in sidewall height between a 30 and a 35 will make any noticeable difference in traction. However it may make a difference in ride quality. Go with the 35.
going with a wider rim and tire are not going to help your unless you run a better tire! On my 98 cobra i run 18x10 rears with drag radials on the street. With a power adder it will still break loose. Its just the nature of the beast. :SNSign:
I ran 315/35/17 on my 10.5" wheels, and that seemed to be perfect. If you run a 335/30 you will be closer to the proper overall tire height so your speedo will be accurate.
And like someone said, just changing tire size is not the way to gain traction. Sure a 335 gives you more contact patch than a stock 245, but its all about the quality of the tire.