It should say on the side of the 17" tires what PSI you should be running. I do not know for sure but I would assume 19's are going to have more PSI than the 17's just based on the side wall being shorter.

 

I have been using Dunlop Wintersport M3 Snows for the last 5 years....I went with 17" tires 225/55/17 on all four corners, put them on ASA KA3 17x7.5 rims. I have no problems with traction/VDC ..... dry handling is great...ride is better than my summer performance tires...they are quieter as well.

I went with the same size so i can rotate them each season.....I have found no adverse effects losing the stagger for this set up.

The 225/55/17" seem harder to find now a days...but they are out there.....
Good luck

 

OP, I've been running 225/50-17 front and 225/55-17 rear for 6 winters and this is the combo that Tire Rack originally recommended to maintain OEM diameter difference, and these are very close to OEM 18" or 19" sizes. It works great.

As for tire pressures, those should remain the same as stock, regardless of wheel or tire size. It has more to do with the weight of the car than anything else.

 

There are several "all season" tires for the 19's.

I'm pretty sure you can even find "winter" tires.

http://www.discounttire.com/dtcs/fin...Form&rc=CAOINT

 

I had Dunlop Graspic DS-3 on 17s as winter tires for the G. Handled great; never had an issue. 225/55 set up. Just common sense in driving during the winter and you'll be fine. Hope this helps!