Down in frigid PR, you don't need a 0w or 5w anything. You don't need that much vis spread down there. I am generally not a fan of wide spread lighter multivis oils in heavily modified street and/or track engines anyway. If that's what you have. If your engine is closer to production, then the generic FoMoCo Xw-20 recommendation should be fine.
A tighter spread 10w-30 full synthetic "should" be good for hard street duty with your mods down there. Like the others, I would go with Redline, which will give you better film strength at the viscosity as extra insurance, or at least an A3 oil. Don't convert over until you have several thousand on the clock.
If you eventually run a turbo, then you absolutely want to stick with something such as RL, and maybe even consider a borderline 40. Anyone recommending a 20 on a modded out aftermarket turbo setup without knowing more is playing russian roulette with your engine.
This is all suggested based on averages, without knowing the actual bearing clearances or valvetrain particulars. I agree with some of the others that these are also very vital considerations, independent of temps. I'm guessing based on industry practice that a higher output track-tuned block is more likely to have wider clearances than the standard variant. But Ford has gotten goofier in recent years.
An auxiliary cooler is also a good idea.
