the best way to save money is to tune each machine to the least amount of errors ...and as for your question about S3 and S3+ since you know about the difference there...you should know there are way more than 2 variations of S3/S3+ (more than 10)
Have some fun and get a tester to see what each machines output max is....and it doesn't have to do with set clock speed and voltage as you will find out...
From what I have gathered but not tested/verified is that with the last firmware update for S3/+ that voltage adjustment is disabled so don't use that firmware....
Sorry I cant help I don't have any S3 left but no 2 machines run the same....I know because I tweaked at least 50 S3s for best output before they went on their way but then the price of bitcoin was more than double what it is now so power was not an issue
If your machine is clocked at say 500GH/s and submitting less shares than one clocked at say 231 then its time to adjust....oh the joys of mining
