Yeah, eBay does not return much. For me, it's one of those right place at the right time (and having the cash) kind of things I think. Window shopping is still free though!Someone I know had one of those 2GHz cards, he sold the computer although I did try to buy the processor!
The card I have is actually a dual 2.0. It's got the switches for it, but I've just never been able to get 1.8 stable for very long. And the 2Ghz setting forces a boot into Open Firmware. You can get out of that by telling the Mac to boot of course - which it does, right to a kernel panic. So, I've settled on the 1.73Ghz setting, which is actually 130mhz faster than what it was advertised at (1.6Ghz), so I can't complain much. The card is dual 7447As though.
I'm not sure I'd want one of the NewerTech cards. I found their installation PDF and it says that you have to use an OF hack to run the processor card. That's fine, but the downside is that you can't boot from any disk that does not have their kext files on them. That means you have to boot from customized OS X installers and customized DiskWarrior disks, both of which you have to make yourself. And if you reset PRAM, NVRAM or reset the logicboard/PSU you have to go through the whole OF hack all over again because it gets wiped!
I'm not a big fan of the Giga Designs card I have in the sense of how it has no L3 cache and no stepdown capability (Low CPU versus High) and also no nap ability. However, they at least got the OF thing right. I can boot from any disk.
So far, it seems to me that Sonnet is the company that got things right. I still have my old single 1.2Ghz card. Sonnet is of course always expensive, but I'm starting to think they're like Apple. You pay more, but you get lasting quality.