As said already... speed isn't everything. If a "noisy" fan-cooled hot-running machine isn't a problem for you then compability is the next big hurthel. I can easily say if I was you I'd either go for the 030 for optimal compability or if speed is a big criteria skip the 040 and go hunting for a 060 (the 060 also got back much of the compability you lost with the 040, though obvisly not all).
Only 040 card I'd concider for the A1200 would be the BPPC040(full) as it have some other positive sides that overpower the downside of a 040, but that card isn't realy practical for a desctop machine (but if you're looking to get mediator you're also talking tower and then that isn't a problem).
