Well I've had no problems with my HDD on BF3 despite not having an SSD. I forgot what settings I had it on when I last played but they were up there.
So that may not be entirely true. (The bottlenecking, not the loading system)
You wouldn't know.
Unless you've run a computer with an HDD and that exact same computer with an SSD on the same settings in the same server at the same ping, you wouldn't be able to factually say one or the other. However there are people who have run tests on realtime loading and saving, and it has been seen that in builds with higher end parts a standard 7220 RPM HDD will cost you about 5 FPS, of course this in a scenario that the entire game basis itself around a constant loading/saving cycle, but in BF3 unless you're online it doesn't happen.
Trust me, I've been around the computer world quite a bit, and I know what I'm saying to be true, I wouldn't be saying it if I wasn't confident in myself.
I was given an $800 budget and it was apparent that that /was/ indeed the budget. On that budget it is not sensible to boot and run priority applications off a 7200 HDD, it is sensible to buy a low GB SSD and boot from it.
On a $650 budget which is /totally/ different, it is not sensible to invest in an SSD, rather just a better HDD
So don't let it seem like I suggested something for a build that is wasn't reasonable in, if you don't give me an accurate budget don't expect be to build you an accurate PC