The problem with Co blends of sweeteners is the synergistic effect that they have with each other. In combo they have a combination 1 +1= 2.1. This is found in Sensory evaluation as Roy stated. Equivalent sweetness in relation to sucrose is singular referenced. Commercially the strength of saccharine is specification based 450x or 500x and within a range in relation to sugar and Sodium Cyclamate is 30x stronger than sugar. If one changes supplier, new tests need to be carried out. This you would need to have in commercial world . The trick is you need to know a starting ratio to these two, plus there are defined ratios in country food laws of how much each sweetener can be used, a 1g of cyclamate in my country, so 30g of equal strength sugar can come from cyclamate and other 50g per Litre equivalence can come from saccharine depending on strength you will start with. . Cyclamate is the better tasting one of the two, as Saccharine has metallic taste in it. With synergy of the two, you will expect to use slightly less of the calculated amount of saccharine either the 450x or 500x strength. The curve provided is a starting point I believe and should not be discarded as it gives you a mg/l equivalent relative to sugar and your required starting point is going to be g/l in beverage for the 8 % (80g/l) also expressed as Brix. There may be other cyclamate and saccharine types. Lastly a beverage is also acid/sugar critical and buffering of acid, plays a role in artificial sweeteners.If it has to be 50/50, then 40 (4%) equi strength must come equally from cyclamate and 40g (4%) equi strength from saccharine and the strength of each is built into curve and synergistic effect is not taken into account. So values needed are indexed at 4% level on each curve. You can solve the mg/l amounts then.