Thanks for the suggestions, guys.
Ideally I would like to go for a fresh install on SSD, it makes perfect sense. But there are a couple of problems, least of which is the fact that it will be utterly time-consuming to install both OSs, all the necessary programs on both and update Steam with game installation folders. However, my main concern is that I have upgraded Win10 from a genuine Win8 key..and now that Win10 free upgrade program has ended..I am unsure if the activation of Win10 will go smoothly. I am not saying it cannot be done, but mostly it will involve pinging MS call centre reps. So more headache..!!
Comparatively, cloning of the OS seems easy and fast. And once that's done, I can simply format the C and D partitions on the old HDD, so there won't be a conflict of boot loader. But even without that, as *Lincon_WD* said above, I think the boot loader will be read from the first disk that's configured in the BIOS.
On a related note, does anyone know how's the quality of Zotac SSD? 240 GB is available for as cheap as Rs 3200 @ Primeabgb as a bundle with Gtx 1060. But before buying that, I'd like to know what others think about Zotac..