You may not like the longevity of the .35S on your proposed(?) 0 nitro-20 oil mix. Especially if it comes out of the jug your followup reply describes as all-synthetic.
In contrast, you say it "runs very well" on 5n-28castor, so if you are going to use it much, and have already gotten comfortable mixing fuel, just mix what you need, and enjoy the trouble-free performance.
Switching to less oil will mean less lubrication for the big end of the rod. Trying to increase the compression to get back the power lost by eliminating the nitro may end up with different impulse loads on the rod bearing. If the engine already has the brass-bushed big end, that would improve your odds. If not, stay curious--about where to find a replacement rod.
Dave