If your motherboard has only SATA II (3.0GB/sec.) then both drives will have very similar performance.
However, if your motherboard has SATA III (6.0GB/sec.) then the Extreme can use its full speed which is nearly twice as fast as the Ultra.
Also, on SATA II connection, the small file performance (~4K) is improved 10%-12% when using the Extreme.
Also, you can buy a $25 add-in SATA III controller card for your SATA II motherboard. It will fit in a PCI-x1 slot and allow the Extreme model to give about 50% better performance than when it's connected to a SATA II socket. An add-in SATA III card that let's the Extreme reach its full performance/speed will cost around $99 or more and plugs into a PCI-x4 slot instead of the slower PCI-x1 slot.
I own both models and feel obliged to tell you that in everyday use there isn't much noticeable difference because most of the things we do all day aren't demanding enough. You might notice the Extreme is faster for certain tasks such as opening/editing/rendering huge video files or splitting huge RAW photo files into several "layers" in Photoshop then applying filters/effects or maybe a little bit faster when loading some of the newer games out there (although the initial "disk-check" delay can be longer than the game loading time !).
The really big noticeable difference is when you switch from a regular hard drive to any good SSD.
Finally, the Extreme model has come down in price now so buy it even if you don't have SATA III yet. You'll get very good performance right now and see even more speed later if you upgrade your motherboard.