This is a sample of the Darlingtonia seedlings I have on the go at the moment. These are all a year old and can be clearly seen in a peat mix, not so obvious is that they are over / in a sphagnum lining. I have trays in full sun, part shade, full shade, in with solar pumps and without. The same applies to the seedlings I have growing in Sphagnum.
So far there's not a great deal of difference except the ones in Sphagnum have to get taller a lot faster.. Those in peat stay compact.
I do have a couple of trays where They were in Sphagnum and I've transferred them to peat. We'll see how those progress over the growing season.