Yes, I can.
For my Coolpix 990, I have a 128MB, 256MB and a 512MB CF card.
The 128MB is an Ultra1, 256MB a Ultra2 and the 512MB an Ultra3.
The difference is noticeable!
I don't like the 990 when I'm using the 128MB Ultra1, it's not that fast on the write.
The 256MB Ultra2 is much better and the 512MB Ultra3 is the fastest!
I have the same with my Coolpix 885 and Coolpix 5700.
So, yes there is a difference!
With my Coolpix 2100, I only use a 256MB Ultra2, because I've found it's the best!
You can test this for yourself, put a CF card in your Coolpix, start a timer and make a picture.
Then press the shutter button again and make another picture.
When the timer is running, press the shutter button again and make a third picture.
Then look at the timer and see how long it takes to make the third picture
.