I have a G-Force T5 rated to 500ft lbs. It shifts great, and is much lighter than a TKO. That being said, no, its not as strong as a TKO. I ended up with the G-Force because I got a good deal on it. If money was not a problem, I would get the Astro A5 for my application. If it was going to be a big cubic inch Windsor, I would go with a TKO, no question about it. I am not pushing the limits of my G-Force at my power level, but I believe you would be right at its realm with 450rwhp.
As far as the T5 can't hold the power theory, I'm not totally sold. Its about like a stock block, some break and some don't. My father-n-law has put hundreds of passes through a straight cut G-Force geared T5. 570fwhp, 6500rpm clutch dumps with a Spec Stage III clutch. The trans has never even been freshened up. But, this is not a street transmission and is really not in the same class. I just mentioned it because it still utilizes a stock T5 case.
Joe