If i was doing it i would clamp some stops on your drill table to locate your box for the first hole, grind the drill flat bottomish so the drill cuts initially on two points (each flute) use parafin as a lubricant and don't go silly with the revs, just cozz you can cut ally at a fast speed doesn't mean you have too, drill your 25 off @ 7mm. reset your stops and do the 8mm.
Simples