Replacement Perennial

I've just dug up a big clump of montbretia that hasn't flowered for a second year now so decided to get rid. Now i'm looking for a tall perennial to replace it. The space around it has 3 shrubs ( 2 potentilla yellow and orange and hypericum hidcote). Sun up to about 3pm, normal/clay soil. I was thinking of Russian Sage or something similar. Any ideas welcome..