I wont comment on what hyde12 said, as you didnt specify your situation, so I wont judge or guess your actions.
To give you some idea, Im pretty sure that 7.5g gel a day will only yeild something like 52mg a week total test. But remember 100mg of inj. test only actually yeilds like 70mg or something like that, so it kinda seems like an apples to oranges kind of thing when simply talking about mg amounts.
And Im not really sure how that will interact/combine with test e, but normally since androgel has such a low dose, its not considered a valuable viable form of test for enhancement. However, your situation may yeild different results as I have seen no data on someone using both the gel and the injection at the same time. And furthermore, depending on how much gel you can get, it may be a way to help keep your levels at a more stable amount between injections. Im speaking hypothetically, and talking about amounts at or above 10g a day, ie: 12.5g, 15g, which is well above the maximum recommended dosage, and would be a whole heck of alot of gel to be applying everyday. You could always split it up throughout the day, but this is all conjecture as I have no idea if you could even absorb 15g a day effectively.
Sorry to run on, but I hope Ive given you a least some direction on finding your answer to your quesiton.