Choice of speed is fairly simple; 10k for all the tool sizes.
Using coated carbide on 6061 is not optimal but if you have flood coolant it will be okay.
The thing you will need to watch is your depth of cut, width of cut and feed on the 4 and 6 flute cutters. These do not have much flute clearance for chips, especially the 6 flute, so you should keep the feed per tooth smallish such as 0.002" or maybe even less, the depth at not more than about half the diameter and the width of cut not more than about one third of the diameter.The lack of chip clearance is exacerbated by the coating which can make 6061 tend to stick and build up in the flutes until you just have a blob of aluminum spinning around.
Incidentally if you can do it, boost the coolant concentration up to something like 10%, assuming you are using water soluble coolant. This can help minimize the sticking problem.