Revisiting My Grandma's Quilt - Block 5
18 count mono canvas
Block 5 is an interesting one. It combines two different stitches that behave very differently with the different threads.
I started with Perle 5 - and quite like it on the 18 count - the backstitches are dense and the center Rhodes has nice coverage.

I also don’t mind the perle 8 - the center Rhodes has a little less coverage but I like the canvas peeking out.
The Perle 5 is Caron Watercolours and Perle 8 is Caron Wildflowers - both in 016 - Bark.
Stranded silk - 3 strands - is also very nice. The silk threads lay flatter than the perle, but the silk is lovely. The coverage is similar to the perle 8. You could use 4 strands with the center Rhodes and that would increase the coverage.

24 count congress cloth
I tried 2 strands of stranded silk (Caron Waterlilies 180 - green Tea) on the 24 count and I was very happy with it. I think you could try 3 strands on the center Rhodes for a little more coverage.
For comparison, the original piece is stitched on 28 count Jobelan with 2 strands of Gloriana Fallen Leaves.

Notice how different the two dye-lots are with the Gloriana?! The newer threads are MUCH deeper! More on dye-lots later.
I will be auditioning different Caron Waterlilies colours for the re-stitched pieces. This is a good opportunity to try different thread brands. This piece could easily be stitched with Cottage Garden Threads, Chameleon Threads (from South Africa), Threadworx, etc.
The only caveat is that you should try to use variegated threads with 3 colours.