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The problem is just that the Samsung burner doesn't think that your discs are good enough for 52x burning, so it's limiting them to 40x. There are some discs out there that it will burn at 52x, but it isn't going to do it with the ones you have.
It turns out that Lite-Ons have better media compatibility than most drives, which is why your Lite-On was burning your discs at 48x.
I must admit that I'm partial to Lite-On, but I have to say that I think that the best idea would be to re-install your Lite-On. When it comes right down to it, burning at 52x won't be even 10 seconds faster than 48x, even with a full disc. If you burn discs that aren't entirely full, the speed difference will be even less. Or, you could keep both in your PC! That will work fine; I currently have two burners (LTR-12101B and NEC NR-7800A) in one of my old computers and three (Lite-On LTR-48125W and two Lite-On LTR-52327Ss) in my main computer, and everything works great that way!