Having recently purchased a Rebel XT (not the XTi) I can honestly say the XT series are really great cameras. Like yourself, I was caught between getting the better camera and getting better lenses...I really wanted the XTi, if for no other reasons then the larger LCD and the higher megapixels, but I was faced with getting the XTi with no lens at all or getting the XT with at least an extry level lens or two...wasn't really a hard choice since a camera doesn't do me much good without a lens. Beyond that, even if price/money hadn't of been a factor, I really wouldn't have considered the 30D's for what -I- shoot (which is mainly animals, wildlife/nature, scenics/sunsets, etc., although I'm starting to get into weddings and such now too).
As Bob said, the size issue is really a personal thing...personally I'm 6'2" and I really like the smaller size of the Rebels. The size of the XT's/XTi's is very similar to my old Canon FTb and only slightly larger then my beloved Sony H1, so it was very comfortable and quite familiar to me. Further, to me at least, even if size really were an issue, I can't say it would be enough of an issue to warrent the extra $600+ for the 30D. With that said, I should also mention that I really don't care for the silver body of my XT, but it wasn't -that big of an issue- for me to spend an extra $20 to get a black body either...call me cheap, but I don't like paying extra for "aesthetics"
. Now aesthetic issues aside, the XTi's pretty much match or surpass most of the features on the 30D's...same processor, similar imaging chips, etc.., Yes, there are some minor differences, such as the view thru the view finder, but over all, they are quite comparable, except for one important factor...speed.
Since you stated that you're looking for something for "fast action shots", I think the biggest factor you may need to consider is really that of speed. For what I shoot, "speed" isn't really all that important...my Rebel XT pretty much shoots "as quick as I can click" (even with the cheapy PNY memory cards I use) and I almost never use "burst mode". Once or twice I've had to wait a second or two for the buffer to transfer to memory, but I've never "missed a shot" because of it. In fact in the digital realm, I had been using a Sony H1 and an Olympus C-4000 and in my film days I used a Canon FTb (all manual), so the XT is in fact much faster then what I had been used to. I can get good pics of my dogs running thru the park for example and the camera is more then fast enough for that. On the other hand, I don't shoot sports...if for example you're going to be shooting stuff like high school football games where you need to fire off -a lot- of pics in burst mode to get that shot of the winning pass or touchdown, flat out, the 30D is a much faster camera.
All things being equal, I'd easily go for the lenses over the added price of the 30D...for myself at least, the price of the 30D's isn't really warrented by the features compaired to the XTi's (even if I had the money! LOL!), but again speed isn't really a big factor for me. I think the question you're going to have to ask yourself is simply "how fast is fast enough?" and that will probably be the determining factor for you.
One last quick comment...the "8x10 work". Either camera is going to produce great results for 8x10 and larger. As was discussed in another thread in these forums, don't let the lab guys bullsh*t ya, I've been getting really great 8x10's and larger
from my 4 and 5 megapixel cameras. The 30D and the XTi are both going to produce great images even at large poster sizes such as 24x36 and beyond (assuming of course it was a good picture to start with! LOL!). The size of the prints in regards to these two cameras shouldn't really influence your purchase either way...they're both great
Okies, I'm going to wrap this up now. Again and simply if speed weren't an issue, I'd whole-heartedly recommend the XTi in a heart beat, but since you stated you're looking to do some "fast action" stuff...might be worth putting some more thought into before you purchase.
Just my $.02 worth...don't spend it all in one place!
Bright Blessings & Gentle Breezes,