Let's see...
First, I'd highly suggest switching from Audiocatalyst to
Audiograbber. I was using Audiocatalyst for a long time, until I found Audiograbber. I think you'll like it much better. It fully supports v2 tags and is much more feature-packed. I've got a feeling others may chime in with their own personal choices, but Audiograbber is nearly identical to what you're currently using, so it doesn't require much of a learning change.
That aside, to retag using filenames in Tag Studio, you'd use the "Auto write tags based on filenames" tab. That, you probably figured out already.

You'll notice that there is no option for choosing an ID3 version there. The reason is that the ID3 version is a "global" setting. If you go to File --> Settings in Tag Studio, you'll see an option that says "Primary ID3 version", with two radio buttons for each ID3 version. For your situation, you'd select "v2". Immediately under that, you'll see a box labeled "Perform write operations on both tag versions when possible".
Straight out of the help file in Tag Studio:
In reply to:
Perform write operations on both tag versions when possible:
When this is active, all writing of tag data (except from the browse/edit tool, which has its own settings for this) will be made to both the ID3v1 and ID3v2 tag of a file. Otherwise it will be written only to the tag with the chosen primary ID3 version (see above). E.g. if you only want Mp3/Tag Studio to write ID3v1 tags, like in earlier versions of the program, simply choose v1 as primary ID3 version (see above) and uncheck this setting.
So, if you check "v2" as your primary ID3 version and
UNCHECK this box, it will ONLY write ID3 v2 tags.
I think most programs nowadays read v2 tags and then revert to v1 tags if the former doesn't exist. Originally, this was the "detriment" to using v2 tags... not every program supported them. I don't think there are many programs that don't support v2 anymore, so you're probably safe. If you do find one, you might want to upgrade the version or change programs, as it may run into problems with the MP3 files. The most obvious reason people use v2 tags is because it broke the limitation on the use of long track names.
Personally, I write both v1 and v2 tags, so that I know if a program is having difficulty with the MP3 file and can do something about it... yet it won't stop me from knowing what track is playing. It's all personal preference.
Hope this helps!