second 7300 or ati?

I currently have just one geforce 7300 gt in my 2.0ghz mac pro. It struggles. Should I buy a second 7300 and run them in sli mode (which is possible yes? and in windows more importantly?) or the the 512mb ati card the replace it with. I've no idea about prices for these, could someone (in the UK) enlighten me? Where can I buy them as well? I've only had a quick search online, but I didn't spot any apple formatted cards...

thanks

A 2nd 7300GT would be the cheaper way to go. I just saw one sold on eBay for $53 USD. I didn't want to bid that high for such an inferior card (and yes I own one.)
I am not sure what SLI mode really is seeing I haven't used Windows in a year and didn't own a computer that supported SLI. So I can't help you there.
The X1900 is a far superior card. I did a google search last week and found a few places selling the Mac Pro version for $379 USD.

An X1900 will blow away two 7300s in SLI mode. So if you want to play games or just need lots of 3D horsepower, go for the X1900.

One Link (Canadian)
Cheapest Link
Nextag Comparison Site

I would think that if the rumors are true and the new Mac Pro comes out in March or sometime around there, the will be new, faster video cards in them. I haven't kept up on all the newest technologies but it would seem likely the new video cards would work in the current Mac Pros.
Only Steve Jobs really knows though.

The ATI X1900 is more money but a great video card. I have it and love it.