The 700R4 transmission is a popular choice for many high-performance vehicles, but it can be tricky to get the perfect shift timing. The optimal speed at which your vehicle should shift into overdrive depends on several factors, including your engine's power output and how you plan to use the vehicle. Generally speaking, most people recommend shifting into overdrive when the engine reaches around 2200-2500 RPMs under normal driving conditions. This will provide smooth shifts while also maximizing fuel efficiency. If you're using your vehicle primarily for racing or performance driving, then you may want to consider shifting up earlier – around 2000 RPMs – as this will give you more responsive acceleration. It's important to note that these are just general guidelines; ultimately, it's up to you (or a mechanic) to experiment and find what works best for your setup in particular.