The upgrade I chose was the best bang/buck ratio; the Sonnet G4/ST upgrades will take me to 1.7GHz, but at $499, that's too much.

Sonnet's 1GHz upgrade is $229 versus the $189 I paid for the PowerLogix. And with the exchange rate the way it is, that's about \ufffd92 :-)

I did look on eBay before deciding to buy new and came up blank both that side of the pond and this.

I bought it from OWC: [link|http://eshop.macsales.com/item/PowerLogix/PF55SQ10002M/|http://eshop.macsale...gix/PF55SQ10002M/]

I'll report back on fitting (that BGP socket looks like making this a doddle) and performance.

If I were you, I would definitely consider scouring eBay for something with the following rough specifications:

Faster than 400MHz G4
More than 384MB RAM
OS X installed (10.3 if you can get it)
No more than $400ish

If you're patient, you should be able to do MUCH better than that.