Humalog is very fast acting and probably one of the safest if you must use slin. 5 iu right after your workout. If you don't keel over, after a week up it a couple of iu's per week maintaining that you feel like you can handle it. Ingest 20g of carbs per iu immediately after injection. (better be safe than sorry) If you don't ingest the carbs the insulin you took will eat up all the glycogen in your blood stream and your brain will have no "gas" to run on. It will shut down, putting you into a diabetic coma. You may even die at this point. If you don't die you will be a long time recovering from this type of coma. It's not like a coma caused by trauma, it completely turns your brain off. Then you have to relearn everything you once knew. Given it is a fast learning curve, you will still be an invalid for quite some time. You don't just "wake up" out of this type of coma.
Trust me I know....my brother is an insulin dependent diabetic. He was drinking way too much on St. Patricks day 2001, and passsed out. His goddman dumb girlfriend gave him some of his insulin thinking it would wake him up. Well, due to all the sugar in alcohol the insulin he had in him was all used up and when she injected him he was already negative on glycogens. This put him into a diabetic coma. He was "asleep" for two months, he is awake now but does not walk well and can hardly write or read. He used to be an intelligent man with a college degree. Now, at 35 years old, he is living with my parents so his mother can look after him once again. His thoughts are not clear or consistent and his speech is that of a child.
Now.....if you MUST use insulin, go right ahead. You are a free man and I respect your right to do whatever you want with your own body. But you fuck yourself up and just think how many others you would affect with a bonehead move like that. I am also insatiable in the quest for more muscle mass, I understand and appreciate your fervor. Remember, research is your best friend when attempting to play with this kind of fire.
Look into Vanadyl Sulfate or Alpha Lipoic Acid. They may me all you need for the extra little boost you are looking for.