I have the newer tech card. No problems at all. I highly recomend it. I do a lot of photoshop and its quite nice, even with 40-50 meg files. Whether you should upgrade or continue saving is a harder question, especially with the OS X 's unknow compatability with older machines and the slower bus speed of older machines.
New machines are considerably more expensive.
I have a lot of ram in my old machine so that made my decision easier. I've replaced them with a 233MHz G3 from Sonnet. Just wanted to say that while I loved the twin 604e's, they're dusted by the G3. A specification that will not fit on one page of 8.5x11 inch paper cannot be understood.