Has anyone actually noticed a difference between having fast startup disabled or enabled with an SSD? I haven't.
Depends on your computer. EFI W10 installations boot
significantly faster w/ that flag versus MBR W10. Like maybe 3 seconds versus 10 or so (~450 mb/s SSD), when properly supported
and enabled by your hardware components.
On the other hand, Fast Boot originally found in Windows 8
.0 introduced a
significant delay when you shut down your computer, especially when you have gobs of ram, like I do (32+). (As far as I am aware, it works exactly the same in W10). Fast Boot also prevents updates from being installed
and new hardware configured properly, so a manual or scheduled reboot would still be a must (that's exactly why Microsoft introduced a plethora of wake me up triggers for the updates to be installed alongside that feature during awkward time of the day/night = few people are aware of this actually).
I keep it off, and use S3 (improved sleep), which is even faster but waaaaaay more robust for my usage. It's a great feature for the slow booting 5400 RPMs laptops though (also, not draining your battery), but then again, one might use hybrid sleep, which is on by default (a mix of S3 & S4), on a desktop, I prefer S3 & S5 (classic shutdown) though, manually disabling hybrid sleep, so my system goes to sleep almost instantaneously or shuts down when I need to install some new hardware and/or updates. Currently using a mechanical HDD on my main/working rig (for testing purposes), absolutely, no complaints. W10 loves RAM and makes good use of it (currently cached ~26gb).
Will W10 run faster than W7 on a SSD ?
Definitely yes, by how much? I don't know. You can time and see for yourself w/ a stopwatch. But make sure your video card / network card is supported by W10 before you upgrade. Experience can be negative if the drivers aren't properly* supported by the latest Microsoft OS. Backup is essential as well. Do it properly. I would use a spare hdd/ssd for this type of experiment. I've had mixed results with the older systems and W10. Also, to enjoy W10 properly, plan to get a modern video card (assuming this is a desktop pc) w/ WDDM 2.0 drivers support. It makes a difference even if you aren't playing games, but this isn't a must, just my humble recommendation.
*I've had one AMD HD 4200 blue screening twice a week because of some AMD driver.sys (properly debugged memory dumps). No wonder, AMD doesn't list these cards as officially supported. Dropped in some Kepler card (GK107). Issues gone. Desktop experience feels faster as well. Having said that, I have yet to encounter a single problem w/ any Intel IGP/iGPU I have here. Even ancient WDDM 1.0 certified only GMA 950 working reliably well (not a single halt/bsod yet). They have definitely improved over the years (W10 driver, albeit dated ~2012 provided by Intel by default upon installation). Kudos to Intel.