Nothing that ever came in a Geo would ever be better than a 4agze swap. When a swap actually decreases performance it's generally because of ergonometry/weight of the new motor, or unless it's just some douchebag who wants a K20 in his Supra or some shit. I highly doubt a 4a would throw the balance of your car off to the point where it would decrease performance, considering you're on stock suspension there's not a whole lot of performance to mess with anyway.