Sata II SSD drive in Mac Mini

SATA-I transfers data at 1.5Gbps, or 187MB/s. SATA-II transfers data at 3.0Gbps, or 375MB/s. So yes, you wouldn't be able reach the maximum transfer rate of the 2nd G.Skill drive you posted. However, it should work in the mac mini, though you might have to set a jumper to "downclock" it to SATA-I speeds. You're probably better off getting the first drive.

That's a good question - At what point is buying an ultra-high speed SSD not worth the money on an older Mac with a SATA I controller chip? A few things to keep in mind:

1. Often the quoted performance of solid-state drives is PEAK Read/Write speeds (rather than more real word sustained thruput) so that can be deceptive.
2. Any hard drive SSD or spinning platter doesn't spend much of it's time at PEAK rates anyways.
3. The SATA II spec is backwards compatible. There's no 'jumper' on SSD's that you can - nor NEED to set to throttle them back. Any SATA controller chip in your Mac is simply designed to say; +'Stop. I'm busy. Ok. I'm ready, send me more'+ as data comes at it.

My advice would be to buy a decent MIDRANGE SSD Writing in the 150Mbps range and perhaps peaking Reads near 200: It's going to spend most of its time idle or writing brief bits of data the majority of the time anyways. Save your $$ on a true bleeding edge SSD for the NEXT Mac you buy. But I think buying a low-end 100 Write-150 Read SSD would not keep your Mac mini's SATA I controller as busy as it could be.

Doc
http://www.mac-ssd-drives.com/

I wanted to add - Watch out for the lowest end SSDs like that first G.Skill model you mentioned that were introduced in 2008. Most have an early JMicron controller chip that had occasional write slowdowns cuz they just didn't have nearly enough cache onboard. You can recognize these drives if the spec lists around 130-170 Reads, 90-100 Writes. I own one of these (An OCZ Solid Series) and I love it in my MacBook - and it was cheap. But very occasionally, really only when I'm working in iMovie - I DO experience the slowdowns so many others have reported. It's no biggie, but it's not ideal.

In 2009 models now with better controllers from Indilinx or Samsung - and more onboard cache - you're going to see 170-230 Reads and 135-200 Writes become standard. This is the kind of SSD drive you want for the long haul.