Yes you can run 205/50R15s on a 6'' wheel. Your best combo is 16'' wheels w/ a 205/50R16's. You should be able to pick up a set of 16'' alloy oem wheels cheap. For 17's a popular combo is using the SVT wheels=7x17's w/ a oem size 215/45R17.
Introduce Mr. Torsen to the mix
Bigger brakes then you- D23 crew- D-Tech- Sedan Revolution= #131