If you're properly rolled, it shouldn't matter. Multi-tabling doesn't really impact BRM, but some people do like a little more buffer in their BR especially when they're just getting adjusted to mult-tabling, or adding more tables than usual. The BRM concept is based on having a minimum number of BI's for the stakes you play. It doesn't matter whether you play them one at a time or all at once, from a strict BRM standpoint.
However some might recommend that until you're sure of your success, you might play lower than normal just to minimize losses during that adjustment process.