Insurance Institute vehicle ratings:
Lexus LS400: http://www.iihs.org/ratings/ratingsbyseries.aspx?id=519
Jeep Grand Cherokee: http://www.iihs.org/ratings/ratingsbyseries.aspx?id=341
You can see injury stats for various years here: http://www.iihs.org/research/hldi/composite_intro.html
The Jeep's safety did improve over time -- probably because of requirements to meet more passenger car safety standards as SUVs became mainstream vehicles.
Sorry, I'm a little "hot" on the whole SUV rollover issue this year -- two people in my circle killed in SUV rollovers including a 14 year old in a high speed Honda Pilot rollover on I-70 and a 30 year old in a low speed Jeep Wrangler rollover on a rural road.
I have been using Nokian snow tires from last three years. I lived in mountains of WV and they performed very well. I usually change them from my all season to snow tires around Thanksgiving and back to all season in April.