Given the number of sizes available on the Eagle, it is difficult to get a good quiver right.
What do you think would be the ideal quiver for 75 kilos, 3m, 4m and 5m wings and wanting to cover from 10 knots to 40 or more, both in waves and flat water.
At the moment my quiver is:
690 / 990 / 1290
and I'm hesitating whether a 690 / 990 would be enough for me, or if I could go down the range and stick with 690 / 890 / 1090.
What do you think?

In theory a 690 could be only what you need. It will depend of your objectives ans wing and board sizes. At 15 knts any size of front wing works with a 5-5.5 in my opinion. The smaller the front wing the less range you will have in your wing and board.

790 & 990.

I've used the 790 for nearly 2 years now as pretty much a one foil quiver (have a phantom s but don't use it). I'm 68kgs and have f1 wings 3 3.5 & 4.5 , I would say I need about 13knts with my 60l rocket to get going and have fun. All I do is change the stab if the wave is breaking or leave the Dw stab on for ocean swell and flat water. Maybe I'm just really used to it but I can't find another foil that does it all in the conditions I go out in. It definitely feels a little big on the 25knt plus days and have certainly thought about getting a 690 but it really is nice only using one foil !