[sassan]

How did I miss this thread?

As a owner and in fact mostly use together a 30D and XT (Oversea called 350) I can give some first hand opinion but unfortunately I don't have a XTi (400D) for exact comparison.

Tony one very important feature you forgot to name under "pro", in fact a reason that I may consider changing my XT for XTi is the introduction of "Sensor Cleaning" on XTi that canon added for the very first time on its production line. This is both software (finding that dirt spot intelligently and clone it with adjacent area (As I think it does) and then the "Hardware sensor cleaner" that actually mechanically cause removal of sensor dirt.
I have no doubt that every one knows how dirt on sensor is frustrating and also how commonly this happens. But how good Canon has managed to create this sensor cleaner is the question I need to find in my own way and like to here opinion of those who work with it.

Three or Five frame per second, IMO is a major major difference. It makes that needed latitude, when you need the fast motion captured. So it is type of photography you indulge that determine if it is needed or not. Of course if you only do macro or portrait, you don't need it but shooting model in action, photojouranlism, bird shooting, sport event or so on, you will see the difference in terms of winner or looser image. it is a 40% difference and in my hand a very significant one. 20D and 30D are among the very few Canon models that give you this speed even very much higher priced bodies don't. To me MK III's speed is a bit dreamy for now, but 30D is a must. One very important thing here is the size of buffer as if small, and you fill it up quick, then there is no real use. Also note that 20D only gives you 5 fps but 30D gives option for 3 or 5 fps. Another really good feature as I commonly noticed with rapid 5 fps, I do take more excessive, not needed shoots. Seems like body can't act fast enough for these machines.

In a bird shooting photo session on one weekend morning at pier when I was in a constant machine gun use of burst 5fps mode, (Dan is gonna laugh at me now...) I successfully managed to kill my 30D when red access light was constantly on and nothing else was working. To make a long story short, being under warranty still, my beloved 30D had a vacation at Canon's factory center that fortunately is only one hour away from where I live. The magnificent thing that happened was for me to learn how nice, helpful, polite and even passionate these Canon personal are. I was too impressed with kind of care I got. Adding that to a turn over time of 5 days. Gush there is even more reasons why I love Canon...
Take home lesson for me, though you have, use it wisely and only when needed. No this is not a Cine-camera.... But to say if it is a useful feature or not, I say YES firmly.

Two extra megapixel? Well here I laugh. After introduction of 2 MP pictures (When I learned how to struggle with 0.5 and subsequently 1.3 MP image resolution), I really never saw any difference in quality. Well I am not one who shoot to make a billboard size enlarged picture or poster.

One very important thing you need to keep in mind is that Control Bottoms and ergonomics of XT and XTi or 20D/30D/5D are very similar. You may hardly figure out which one you are using as you have one of the two series. But when mixing for eg in my case XT and 30D, you constantly need to struggle to fine how to do what, on every switch between the camera bodies. I remember very well on first days of owner shipping 30D, how hard everything, for eg change of ISO, Costume WB etc was, when you go for familiar locations from your other camera.

Feel of camera; Sure different but IMO small and light is an advantage. If you need the rough rugged feel of 20D/30D just add a power pack to XT. You will be very satisfied.

Now finally to answer your simple question;
I don't think XTi is a good substitute for you. Not to say I think any less in terms of quality you get from XTi but just its the combination that needs to be complimentary in my opinion.

My Suggestions:
1) If money is not an issue, go for 30D as backup.
2) If so, think of buying a used 20D that you are completely familiar with. Thanks to new brother introduced, the 20Ds price is significantly dropped. You may even fine a new 20D for dirt price if your camera shops inventory permits.

Out of topic: But I was curious what made you to think in your scoring scale, to give a 10 to Pentax 10K? In other words is it to give a 10 or get a 10 (Now Duncan is gonna hate me).