100% in one tech until complete is the optimal setting.
Eg.
Say you have 4 areas of research, the next level in each costs 1000 gold.
You have a budget of 100 gold/month.
If you set 25% into each of the areas, you will progress 1 level in each area at the end of 40 months.
However if you put 100% in the 1st area, then in to the second when the first is finished ...
then you would get level 1 in area 1 finished in 10 months, area 2 finished after 20 months 3 in 30 months and 4th area in 40 months.
So either way you get one level in each area after 40 months, however with the second method you get the advantages of the new levels up to 30 months sooner.
And if those advantages, earn you more money, then you will complete the other levels even sooner.
Eg.
Say you have 4 areas of research, the next level in each costs 1000 gold.
You have a budget of 100 gold/month.
If you set 25% into each of the areas, you will progress 1 level in each area at the end of 40 months.
However if you put 100% in the 1st area, then in to the second when the first is finished ...
then you would get level 1 in area 1 finished in 10 months, area 2 finished after 20 months 3 in 30 months and 4th area in 40 months.
So either way you get one level in each area after 40 months, however with the second method you get the advantages of the new levels up to 30 months sooner.
And if those advantages, earn you more money, then you will complete the other levels even sooner.