While not using a Marlin XL7, I have been getting great results with believe or not.....Reloder 25 and Sierra's 120 gr HPBT, this load shoots in the .3's in my Cooper M22.
Winchester Brass
Sierra 120 BTHP
57.5gr R-25
215M
OAL 3.200"
Averages 3110fps out of my 24" bbl
*NOTE*
Alliant's max load is 58.0 grs with R25. I went to using the 215M's due to me running low on the 210M's. I did reduce my loads and worked back up and found out that I gained appx 25fps using the magnum primer over the standard.
I am really impressed with using this slow powder in the 25-06 as it's velocity is a bit more than I was able to achieve with my favorite, R-22. I would be interested in others trying something like this and see what results they get.