In my considered opinion, if this is something you are needing to do on any type of regular basis, then you need a specialized tool that does what you are asking. Not a text editor that has search capabilities. The editor would have to load the file. I personally think you would be best leaving the file on the drive, and allowing a stand-alone compiled program search line by line, placing those lines into a new file that it finds meeting the criteria.
This would require a relatively small amount of code, and is something that could be run from the command line or a batch file to repeat the process on a recurring basis, changing the text to search for each time as needed. Or perhaps better yet, a small Windows program that will ask for "text to search for", "file to search in", and "save as filename".
Nothing will be lightening fast on files that size, but a compiled program using C, C++, C#, or Object Pascal will give you the fastest possible solution for what you are looking for.
What you are trying to do is called "Data Mining". Data mining is best left up to optimized, specialized programs. UltraEdit was created to write such specialized programs, not to do the actual data mining.
If you need such a program written for you, I would be willing to help. I can't charge anyone else this year, because it would throw me into a higher income bracket and I'd pay too much in taxes, so this is better timing for you than for me. I would have to do the project "pro bono". I have a bit of spare time this week, but probably not after this week. If you are interested in having this professionally handled without charge, you may contact me on my contact page
Why do I offer this? I like helping out the UltraEdit community from time to time.
You may also wait and see if anyone else has another idea. You don't need to respond to my post, except by contacting me if you decide to do so.