Hi, Jrstech! Well, let me see if I can help you find this out. Is it a Momentus 7200.4? Apple has been using a lot of Toshiba drives for its 500GB 5400rpm configurations, including the Mac mini with the Core i5 and the AMD GPU that you have as well as the new 2011 MacBook Pro's. I don't like the Toshiba 5400 drives, as they are mediocre drives. They used 500GB Seagate 7200rpm drives in the high end mini, although in my case, it doesn't matter anymore, as I finally installed my 2nd OWC SSD. Rest assured that you have made a significant upgrade to your machine. I say this with such confidence, because that's exactly what I did with the Toshiba 750GB 5400rpm drive that I found in the 2011 17" MBP that I had for approx. 2 months, which retails well over $2,500 without tax. The first thing I did was upgrade it to a Hitachi 7200rpm drive and while it is certainly no SSD, the difference was significant enough for me to feel it in day-to-day use. And this is also where a quick response to the OP's revised...
I second Daniel's post as to how there are not only no proprietary thermal sensor to be dealt with, as you can see in the OWC video, but there are none at all to contend with. I just purchased the second of two 120GB OWC Mercury EXTREME Pro 6G SSD's, both with the new 32nm Toggle NAND flash. My plan is to RAID them, so as to achieve a 240GB speed monstrosity that will allow for data transfers of 900MB/s - 1GB/s. To do this, I will have to take the Mini apart almost completely, so as to swap the 2nd hard drive out for the 2nd SSD. I have the server edition of the Mac mini, so the 2nd proprietary SATA cable that is needed to install an SSD or hard drive is already there. I can't wait to find out if it will make a noticeable difference, as just one of these SATA III (6Gbps) SSD's are unbelievably fast. OS X installs in 4 minutes and change. Windows 7 in Boot Camp needs an extra minute or two and booting up is virtually instantaneous. Lion Server (which includes several server components) downloads for me in...
Check this out, everyone! Pretty slick, isn't it? Those are ThunderBolt speeds! And some of the better ones at that! I just got my Mac mini yesterday, and today, I faithfully put 8GB of RAM into it. This is off-topic, but boy does the extra 4GB make a difference when you're dealing with the OS paging to the 5400rpm stock drive. lol... At any rate, regarding the aforementioned article, the trick as to how to get the almost 1GB/s for both read and write speeds is to get two (2) SATA III (6Gbps) solid state drives. Doesn't have to be OWC's. It can be a couple of OCZ's or a set of Intel 510 drives. Incidentally, if anyone has any questions about OS X 10.7 Lion, I think I'll be able to help. I have been using Lion exclusively since Dev. Preview 4 and the installation shouldn't get in the way of this at all. There are a number of different ways to install/upgrade/clone, etc. We should be fine. I've also been an enthusiast when it comes to SSD technology for a while. My first one was the 1st gen. Intel X25-M 80GB...
The ATI Radeon HD 5750 1GB GDDR5 is actually fairly cheap. It's a $100 and if you can find one used, you'll probably pay even less. The 5770 is a little more expensive but quite a bit more powerful because it's a lot faster! However, I am not sure that you can upgrade to a better card. I think you can from a technical standpoint, but remember, the warranty is no good if you put anything other than a replacement of the original part into your iMac. Good luck! :)