Speaking from experience... I have shot both sus and deca at the same time in the same dart. 3 cc or 5 cc depends on how much you are going shoot. if you are taking 4 cc's, then a 3 cc won't work. If you are only taking 3 cc's or less, you are fine. I have taken 5cc's in one shot with sus and deca with no problem. i assume that you will be taking 2 cc's of sus and 1 cc of deca (300 mg per ml). then yes, a 3 cc is fine. I personally would not split those dosages either. I use 500 mg of sus and 200 mg of deca, 3 cc's, and shoot the whole ball of wax at once with great results. The sting from the shot comes from 2 places. Either there is excess alcohol in the sus or excess alcohol on your injection site. The deca helps with the sus problem, if the sus brand has that problem. Let the alcohol evaportate from your skin before you stick yourself, problem 2 solved. I store my stuff at room temperature and don't warm it up before i use it. I also use the same size needle to draw that I stick myself with. It doesn't take long at all. I would say you might save 10 seconds by using a larger needle. I would, however, change the needle after drawing all of your liquids. I was short on darts and did not change ONCE... the needle was so dull after drawing the liquids, that it pushed my skin in and made a loud pop when the dull ass needle finally penetrated my skin. Not a flame to any of the previous bros, just my $.02 and how i run my operation.