I do not see a 305/30-20 in my book,, but here are some 295/30-20 is 11.6 wide 3.5 sidewall 27"tall it will fit
305/25-20 is 12"wide 3.0sw and 26"tall ,,255/30-20 is 10 w 3.0sw 26tall 255/35-20 10w 3.5sw 27tall 325/25-20 12.8w 3.2sw 26.4 tall ,,335/25-20 13.2w 3.3sw 26.6 tall and345/25-20, 13.6w 3.4sw 26.8 tall (stock 19" is 255/35-19 10"wide 3.5 sw 26"tall)
any tire with under 260 wear will stick 70 to m80% 200 will stick with a 20" tire about 85 to 90% in this video the tires are close to 100 wear drag radials this was 2013
for street and maybe 2 times a month at the track the stock converter is good