If you are stable I'd keep with that. Altering your meds is no guarantee you'll get sharper. It is quite possible that your meds are the thing that is allowing your brain to work and removing them will cause havok. The stress of additional work along with the stress of changing meds would put you at risk of relapse. I've seen college course work unravel a few people with bipolar. You want to put the odds in your favor. I would consider adding a therapist if you don't already see one for stress management.
As for grades. The biggest thing is that you pass. I have never been asked with what grade I've passed with. A sixty is as good as a seventy. You just have to get the degree. It doesn't have to be stellar. Could you possibly let yourself off the hook with the expectation that you have to do 'really well'. Sometimes it is okay to just do okay.
If you do go off meds make sure it is with the supervision of your pdoc. It may be possible to reduce your meds without going off them entirely.
When I have stopped med my thinking has become dull from depression or chaotic from mania. If you are maintaining now, why reduce your meds. If the reduction is too much your grades would be worse, not better.
I've talked to my family at pretty great length and they insist that me going off my meds is a huge mistake. My oldest son told me that even though I might not feel like I'm as "quick", the other me is really scary. I know he wasn't trying to be mean or anything like that - but it was an eye opener. My biggest fear is that I relapse and have another breakdown. I just feel sometimes like my brain is slowed down and lethargic. I have to really make myself "think" sometimes. I know that sounds crazy but I can just feel my brain not clicking, it seems.
I'm know I'm pretty hard on myself with my grades and everything. I just know that I have to make at least a B to get accepted for the program that I want to get in to. My professor this semester is chaotic and unpredictable - that NEVER is good for me.
I've had a lot of stress at work lately, too, so I know that's not the best thing in the world.
I think I might take your advice and get back in touch with my therapist.