ImageMagick speed Optimization

I'm working on a project to convert a huge amount of TIF files (millions) into Multi Page PDF files... I found ImageMagick and am really liking the ease of use. Currently this is written in .NET Core (C#) so I am using "Magick.NET-Q8-x64 (7.3.0)". I have two questions I guess, first of all how and where in my processing can I optimize to run faster? My solution thus far has been to run in parallel using Parallel.Foreach:

Parallel.ForEach(records, (record) => {
    convert(record);
});

...
static void convert(MultiPageTiff record)
{
    ...
    //Here I basically do foreach file in multipage tiff
    //add to the collection.
    //collection.Write(filename.pdf)
    ...
}

With this solution that I have simplified (since my real convert function has a bit of string manipulation, file finding, etc.) runs and converts at around 1500-2000 PDFs per hour. The size of which range but on average are about ten pages (so originally ten TIF files).

Is there a better way I can be doing this? Maybe a different method of parallel execution? The hardware I am running on is 2x 2.5GHz E5 with 6 cores and 12 logical processors each. My memory capacity is not an issue but that does lead to my next question.

Currently my processing peaks around 6-7Gb of memory! Is this normal? I understand that with the 8bit version of IM a byte is needed for every pixel which is converted, leading to roughly 3.7Mb on a 1700x2200 TIF file.

Any tips would be greatly appreciated!