Haste ring can proc up to 900 ilvl - thats the highest ilvl of all 101 BOEs
Athrog - ive seen 880 max ; Telubis - 885 ; Mir - 885 ; Serrine 880 ; Cyno 885 ; Boughs 880 (very rare) ; Samnoh 885 (very rare) ; Cainen 880 (rare) ; Mavannah 885 (rare) + 880 with socket/leech ; Geta - no idea, i think 880, plus 870 s/l ; Shokell 885 ; Ulfgor 880 ; Gorrog 885, plus not very rare 870 s/l ; Aethryn 890 pretty common ; Fists 890 (very rare) ; Claud 880 ; Welded 880 (rare) ; Vastly 880 (VERY rare) ; Demar 885 (very rare) ; Fran 900 (VERY rare) ; Sameed 895 (rare) ; Eyasu 890 (VERY rare, and always with leech) ; Six feather - 885 (rare) ; Marfisi 885 ; Queen 890 (rare, and always with socket) ; Talisman 885 (rare) , 875 with s/l is pretty common ; Treia 890 (rare) ; Cloak - i think 880 (rare).
very rare - means it can pop on whole EU ah at around 1-2 per month. VERY rare - thats for fran, eyasu, fists, 880s/l mavannah, vastly - they can pop around once per 3 months.