You are right on the money with the 404. My brother has a FN 404 and a restocked ruger 416 rigby. Both stocked by the same stock maker. The 416 wieghs 1/3 lbs heavier but seems to kick 50% as hard.

The 404 has a little less velocity, but more shootability. Perticularly if you wanted a scope in a QR set up. A plus for leapord and other dusk/dawn hunting.

The other plus is you would just need(!) to get a 450/400J 3" double so you would be able to use the same components and only have to remember one set of Kentucky windage figures.

Remember the only reason to get a bolt is to complement a good double. So only buy bolts that scream for the accisition of a new double.