coming from personal experience (I put H11SU Sylvania SilverStar Ultra's in my Terrain) I can honestly say, that there is a 50% difference or more.
Personal experience:
I go to medical school in the middle of nowhere Tennessee and in order for me to shop for food, I must go into KY to Walmart....literally I live in the middle of nowhere, new medical school, doctors a doctor I can care less lol. LMU-DCOM if you're wondering where nowhere is.
Anyways, I baby my Terrain, and in my older car, I had HIDs and was very very very disappointed in the halogen lights on the Terrain. I didn't notice that they were so dim until I got a complete tint on my windows (not the front windshield)
I was driving into KY, and when coming out of the tunnel, 2 nice little deer decided to run across the road. There was no lights on the road, and I literally almost killed Bambi and his friend...literally 3 inches from my Terrain (was a little tired, studying 14 hours a day, but I seriously didn't see them until they were in the street. They took off and almost gave me a heart attack. With al this caffeine IV pushed through me daily lol.
And so I looked online, asked around, and yes, there are some good and bad things to them. They are amazing, super bright, but now, I light up the entire road and don't need to put my fog lights on anymore to feel like I could see. Granted, dark roads and an all black on black terrain tinted makes very little squeeze room for error when it comes to night time driving.
All in all, yea, they might be expensive, they might not last long (I've heard a year or more) but they seriously are bright, and the depth on them are amazing. There has been numerous times since then when deer decided to chill on the side of that road, especially right around now when it's warm, and I can see them every time, from a good enough distance not to freak out if they happen to make a leap for it.
If you buy them, make sure you wear latex gloves. I got mine from Advance Autoparts, and just asked politely if I can get some to install the lights instead of me buying a box of them, not a problem. Installation kind of sucked. My previous car had HIDs that I never needed to replace, and my 69' GTO Judge had aftermarket headlamps that were easy to pop in. Going through the wheel gap on the Terrain took some time, make sure you remember how you twisted on and off the cap, and the Phillips that it came with, the rubber parts of them didn't like to stick to the bulb itself, so I spent a hour trying to put one light back in, not realizing it didn't fit with an extra rubber seal on it lol.