You shouldn't have any rubbing problems with 305-50-20. 305-55-20 will rub a little but my $20 heat gun and 5 minutes fixed that. Get a 25mm offet and 9-10" wide and you'll be fine. I'd get them at a dealer as some rims are wierd shaped and may rub the calipers. I had a problem with a set like that and had to go a little bigger offset. Hope this helps.

22" rims, you want to get 305-45-22 tires. Bigger than 22 and you're on your own. At that point you really start loosing practicality.
Here's some pics of my 20s.