Well, if the relief well offers much less resistance (aka “bigger hole”) then the flow from the current hole should be reduced enough to be manageable.
Problem with drilling relief wells is that it’s a crapshoot. Paraphrasing Dr Michio Kaku from a radio interview on the Opie and Anthony show on XM earlier this week: “You’re drilling 1 to 2 miles, trying to hit a target the size of a dinner plate.”