I recently bought an '07 G35x sedan for my daily driver and I'm thinking about putting '08 G37S coupe 19" rims on it. I heard there might be problems with a staggered setup on the X sedans. Does anyone have any experience with this? The tires are all stock (225/45/19 front, 245/40/19 rear).

 

You can but it's not recommended. Make certain that the front and rear tires have the same circumference/rolling distance.
I recommend you use the search feature at the top of the page, keywords 'Staggered Tires on X'.

Edit, here are a couple for you
https://g35driver.com/forums/g35-sed...ive-train.html
https://g35driver.com/forums/g35-sed...ut-needed.html
https://g35driver.com/forums/wheels-...work-g35x.html
https://g35driver.com/forums/g35-sed...ock-setup.html

 

Another thread on this topic? Again, as long as your overall diameter is close, which in this case it would, you'll be fine. SOME don't recommend it, while others say it's perfectly fine.