I couldn't find much data on the Vectan powders, but I can suggest some better component matches.
The Hornady 200gr PtSpt will be much more accurate, as well as the Sierra's. Nosler only makes 225gr and 250 Partitons which will be superlative hunting bullets but a bit pricey for range work.
Try Hodgdon's BL-C2 if you have access to it. Win.748 is VERY-VERY simular and will give substantially higher velocities than what I've found with the Vectan data I've seen. About 2,800fps with a 200gr bullet at max load of 63.0gr (Hodgdon's data).
I usually start by seating the bullets one diameter depth for most sporting rifles. This usually givs better accuracy than seating to the grooves. This gives the bullets better support and maintains concentricity which is MUCH more important than the jump to the throat distance. For instance, My Weathby Vanguard in .257wby prefers it's bullet seated to "published" depths. IE: 3.170" for a 100gr bullet, and 3.250" for 117-120gr bullets. Accuracy actually goes down as they get "longer", and the throat is so long, a 100gr bullet can't be seated to "touch". Also, my .300RemUltMag MUCH prefers most bullets to be seated to 3.560-3.565", especially the 180gr Nosler B.T.'s. Don't ask me why, as this gun has a rather short throat. A Sierra 180gr ProHunter touches the grooves at 3.595" ! And shoots best at 3.555". Go figure???
I've gotten very similar results to the expanded bullets you show from the very few 200gr Remington RNSP's I've recovered.(MOST KNOCK THE STUFFINGS OUT OF DEER AND EXIT!) I use them in a Marlin M336 in a .35Rem at about 2,250fps (H4895). I had a Remington 760 in .35Rem back in the mid '80's. It was Very-Very accurate with H322 and either the Sierra 200gr RN or Hornady 200gr PtSpt. My Marlin .35 shoots near MOA and has given under 2" groups at 200yds on occasion.
When I finally got around to building my ".35Whelen", I ended up making it a .338/06. Great rifle, but, I still don't have my long dreamed about .35Whelen. With the cost of bullets going up-up-up, I probably will just be content with the .35Rem..........
Thanks for the report and pic's. Let us know how things progress. Plan on using that thing on some Aoudad ???? (only game animal I'm familar with in Spain, besides Roebuck, and possibly stag). Whelen should do well on anything you use it on......