I am an E-5 25B in an E-7 slot. Is this better for my career?

If someone gave you enough trust in you to do the job in that position, it speaks highly of you. Make the most of it, and don't disappoint who ever placed you there. You're always supposed to look two ranks up from where you are, and you're in that spot. Make it work.

Possible. To put this in perspective, I was an SGT in a SFC slot, then I made SSG and all my NCOERs were rated Promote Ahead of Peers, and have been selected for SFC. All of this within a 5 year period. Your career is what you make it.

In of itself, I don't believe that HRC considers if someone does a duty above grade. What will count, and can potentially enhance your career is your evaluated performance while sitting in an above grade role. Make sure you get proper recognition for your efforts on your NCOER. It can even have an indirect influence if your role in the higher slot effects a larger sphere of Soldiers. This effect can be positive for thise sections of your NCOER that relate to intangibles associated with character and presence bullets

EDIT: I do think that Soldiers should be reviewed at the level of job in which they are performing. There is a big difference between the E5 and E6-8 NCOERs