Seeing this thread, I felt inspired to use a rainbow deck in ELO just for the lol-factor. I went from 1109 to 1160 with 6-3.
I can't see myself actually going for 1300 with rainbow, just because it'd get too darn frustrating and I can't be bothered. But winning with rainbow against regular decks is quite satisfying, and is a funny challenge for anyone prepared to try it.
Deck used: Elvis, Melanie, T Gaank, Cyb Lhia, Jean, Murray, Chiara Cr, and Lena
17:01 Elo you lost by default against Quickdevil, TrAitorzZz (2-16): 1307 ELO
16:53 Elo you beat CannabicuS, •●≈ MexiicaN ~ CannabiCuS ≈●• (9-2): 1325 ELO
16:49 Elo you beat Aranais (8-3): 1313 ELO
16:44 Elo you won by forfeit against X YhomaS, Zone X (10-: 1300 ELO
16:39 Elo you drew with O tops, Piratas do Atlântico (3-3): 1284 ELO
16:32 Elo you lost by default against SCI WeeZix, Coconuts Island (8-9): 1283 ELO
16:29 Elo you lost by default against 0-DeMo, PokiMaBuoni (14-9): 1303 ELO
16:25 Elo you won by forfeit against Bone Cr, E X C A L I B U R (7-5): 1315 ELO
16:16 Elo you won by forfeit against SC Koopa, LA SANTA COMPAÑA (14-7): 1301 ELO
in conclusion... tons of 5050 and guessing involved lol