Please don't be too extreme. I want to say a SSD is already perfect for anything, and SATA 2 or 3 only make minor difference. I never said that use HDD is good nowadays.
And I won't shut down my machine as well, not even sleep. However, boot up time is a good real world benchmark for normal use. I don't think anyone of us main workflow is using benchmarking software, however, we use it as a benchmark. Same thing for the boot up time.
I never said go to SATA 3 is bad, I own a SATA3 card as well. However, if I only have very limited budget. I will not get a SATA 3 card but only use a SATA 3 SSD via the SATA 2 port, because that already gave me a huge performance boost. And SATA 3 is just a bonus for a normal user. You deal with very large files which require high sequential read /write and high IOPS. So, you can actually utilise the SATA 3 bandwidth, which is good. But I doubt if OP can fully utilise that too. So I told him just plug the SSD into the SATA 2 port is the cheapest and most painless way to go (NOT best performance), and can still feel roughly the same performance boost.
I didn't say the SATA 3 PCIe card is bad, I didn't say it's not worth that extra $60-80, I didn't say there is absolutely zero performance difference between SATA2 and SATA3. But just share my real experience to OP that I tried both, and can't feel any significant difference. I always told myself that my machine is now react a bit slower. However, I know it's because I know the SSD now is downgraded to SATA 2, I have this concept in my head, but not really feel the difference. Every apps still pops up within 3s (some apps like Photos actually open in less than a second). I just try my best to give OP a objective info.
I am more than happy to hear that you can feel the difference in your workflow. This is why we need SATA 3, or even the PCIe SSD. Because someone like you really need it, and can benefit from it. But since it seems OP has no rush on this item. So, I will recommend him get a SSD like 850 Evo, which is relatively cheap, use that on a SATA 2 port first, if still feeling bottleneck by the SSD, then go for SATA 3. Which will save him some money, and no need to deal with the possible PCIe card problem (e.g. long black screen time during boot, or can't use bootcamp, etc) at the very beginning. Also, he can always buy a SATA 3 card later anyway, it's nothing to hurt to start using a SSD via a SATA 2 port.