"So will 360 HW on Reach release be greater than PS3 HW on GT5 week?"
Well, to answer just that question: No.
Here's why:
Reach launches in 2 weeks time, during a relatively slow time of year.
GT5 will launch in November, when sales should have picked up considerably.
As such, PS3 sales should be higher at that time of year that 360 sales in September, regardless of releases.
Now, I assume you mean the spike caused by both releases. I would expect the spike for GT5 to be bigger than Reach (unless we get a price cut or something, which would skew the numbers). I say this because there hasn't been a full GT5 launch this generation, whereas there has been for Halo. Halo Reach will have fewer new buyers, but I think a portion of the difference in new buyers will be made up by replacement buyers (i.e. current owners purchasing the new 360s with Halo Reach). Regardless of these, I'd expect the PS3 to see a bigger spike, thanks in part to the release of the special bundle in Japan. If special bundles release elsewhere (especially motorsports-loving countries like the UK, Spain, Germany etc) I can see GT5's spike being huge for a week or two, before settling into a relatively minor long term sales boost (1-3k above the norm).
