I have the exact same boat well switch the colors. I bought a Johnson pump and its working great. It is noticeably faster than my jabscos'. The negative is they do not come with the green impellers. However think its still cheaper to buy the Johnson and Green impeller from wake makers. That way you have an extra impeller in case you do burn it up.
The other thing that will drive you nuts ESPECIALLY if you are filling 750s is you will only be able to fill one bag at a time because of the old manifold system. I have the 400s and was too painfull. Ended up putting in a through hull for each pump. Now everything full in 10 mins or less. I think wakemakers has a bigger manifold system if you wanted to do a big 2 inch through hull to a manifold you can.
Others are right even with the 400s in back I want more weight up front. I run 450 in lead in the nose and actually would like another sack in the walk way. That being said 400s in the back 300 kgb 450 in lead and the wake is super clean and nice. Good luck sorry to throw so much stuff out there but your really gonna wanna figure something out with the speed of filling unless you have 30 mins to fill and empty.