Swapping build from Strength to Vit is simply exchanging 35 Strength for 35 Vit, or vice versa. It's literally no different to swapping a 35 Str Slaying Acc for a 35 Vit Fending.

If you're going for a Balance, there's only one answer (which is the expensive answer) - Pentamelds. Five i150 Crafted Accessories max melded for 31 Str and 29 Vit each will give better overall primary stats than any mix of i210 Slaying/Fending.

Generally now though, most DRKs will go 35 Strength in bonus stats, go a mix of Slaying/Fending and as they get more geared, reduce the number of Fendings they wear.

The "optimal" setup is 35 Strength with five Slaying Accessories, but this only works when you have enough Vitality on Left Side gear to be able to survive tank busters. When you dont have enough, substite 1-4 Slaying accessories for 1-4 Fending accessories. There's no right answer to how many - it entirely depends on the encounter and the rest of your gear.