I have 4 VEGA 56 (3 ref & 1 peace of sh..)
I was at 7500-7520h/s and now I'm at 7620-7630h/s with the same "summer" profile (CC:1340Mhz / MC:900Mhz)
that doubling trick doesn't work for me, but I have 7920-7925 h/s without it on 4 vega56 (ref or noname idk, it was OEM and the only sign on it is RADEON), cc 1450-1470, mc 925-935 (found exact stable maximum for each card).