A sedan may be ok with 17's but here are pics of a coupe with 17s arospeed rs gts with 205/40 tires. As you can see the gaps are huge. about 5 inches front and 4+ on rear. Plenty of room for 18s and/or a drop. Again, a sedan is probably smaller as far as wheel well so my only suggestion to you is MEASURE, MEASURE AND THEN MEASURE AGAIN. The car on the pic up there looks like it is deffinately dropped. Knowing what the overall tire size will be will give you an idea of how much space you will have left. Make the car look like you want it to look but make sure before you make a purchase specially on wbay since once they are mounted they will probably not take the rims back. Also, I am surprised you said that you want a conservative look but sporty and will consider a 2" drop. That drop is pretty drastic and will require a camber kit so you don't wear the inside of the tires early. That will cost more $ and if you are concerned about $ you may want to go up to a 1.5 or less drop. Also, if you put springs on you would be foolish not to upgrade to after market struts. The lower profile will compress the strut a lot and they will go fast. Besides aftermarket will prevent from you bottoming out as much. Last comment, remember that a lower ride, specially a 2" drop on a sedan or any other car will affect the ride quality. I have been in cars that are dropped and it feels like I am riding on a the flinstones car with rock tires and no shocks. Your handling will be great compared to stock but the ride will be rough. Something to think about specially if you have little ones riding or will drive the car to work or on bad roads.
BTW- The rims look great! They really look good. What color is your car? I hope they work for you.