Skimmed through the fights from eps 27-46 of the original series:
-ep 35, Marble Screw was able to beat the Zekenna, eps 31-34 had them use the Rainbow Storm to Win, and Juna retreated
-ep 36, Belzei Gertrude (the strongest of the Seeds) did hold off and overpower the Marble Screw, but was visibly struggling and breathing heavily after smashing it.
-ep 39, Marble Screw overpowered Juna
-ep 40, Marble Screw overpowered Belzei (good fight to show that the Marble Screw can over power oppoenents that they cant't match in hand-to-hand)
-ep 41, Juna's power to consume pushed back the Rainbow Storm and was going to overpower it before Pollun stopped providing power and the Rainbow Storm just stopped.
-ep 42, Cure Black (alone), held a punch from Juna. She also was a lot faster than Regine as when she charged at Regine, She left an after image that Regine swipped at.
They also matched in kicks. Cure Black and Cure White were able to be relative in combat to Regine and Juna.
-ep 43, Cures held there own in combat against Regine
-ep 44, The Seeds are stated to growing stronger now (started in ep 43 that they were said to start changing)
-ep 46, the cures were overwhelmed by all 3 Seeds of Darkness
So the Cures growth in strength is an unknown amount times the Marble Screw Muliplier. This increase is less than the boost of the Rainbow Bracelets. They are able to handle two of the three Seeds of Darkness in there base by the end of the series. This also shows that the Rainbow Bracelet multipler is higher than the multipler of the Prism Stones