I know Mayami Hit Pro already and will be reviewing it on my string dedicated thread. What I can say for now is that I really like the string. I dont have experience with 4g so I can't give you comparison but my imagination of 4g is making me say that they are totally different. Hit Pro is comfortable. 4g is stiffer. I have experience only with 1.30 Hit Pro. I had amazing serves with it (best from all Mayami strings I tested so far) , its biggest attributes are consistency, feel and forgiveness of a softer strings but with a more "direct" feel (not mushy, not springy) . Its stable and solid. Works good in my tc95... Depends what you are looking for in a string.
Regarding Big spin x Hit Pro combo I have no idea. I loved Big spin spin potential (obviously) and forgiveness , and Hit Pro for its directional power, feel and accuracy however im not sure how would this combination of strings perform.... I never did a poly poly combo. On paper If I could take their advantages to one racquet and remove the disadvantages this could be a perfect string combo but Im pretty sure world doesnt work that simple