It's am interesting comparison.

I have a TX and an N800 and am amazed at how great and at the same time how bad the N800 is.

In terms of video performance, I reckon the TX with TCPMP beats the N800 hands down. This is why:

TCPMP just works. You do a file open, you get an instant listing of the videos on your SD card, you choose one and it starts playing almost instantly. You can pause it easily and resume when you want, and enjoy the film right through. In fact on one battery charge I reckon to get at least three movies.

Contrast this with Canola, which I use for watching DivX movies (Mplayer is almost unusable in my opinion - you can only move back and forward 10 minutes in a film, so if you get distracted by a stewardess on a flight then you have to spend the next 5 minutes trying to get back to where you where before.) When you open Canola it's touch and go whether it feels like displaying any films you have on your card in my experience, and then only after what seems like an interminable wait. The whole experience is tedious.

The quality of the display is probably better on the N800, but since I've never managed to get a whole film watched on a single charge that's largely irrelevant.

In fact everything is quite sluggish on the N800 compared to the TX. I use a VoIP program on my TX (thanks to a tiny plug on microphone) and you can start it in instant, look up a phone number from Palm's address book and have the VoIP program dial it. Compare that with the (beta) SIP software that the N800 comes with. It is slow to start, you can wait literally a minute for the address book to load if you want to look up a number you have in the N800's contact list, and frankly the whole thing is ridiculous. Skype works quite well, which you can't do on the Palm, but in general I'd say the TX is far better for "standard" applications like VoIP and Movie watching, while I love the N800 for it's ability to run some pretty cool apps like Metasploit and so on.

Take my advice: get both!