“Overclocking” is a mis-used term. You are not increasing the clock speed or the internals of the drive to a high frequency. It’s more like “unlocking” the speed. In the case of making a 40/12/48 a 48/12/48 all that you are doing is unlocking the last 8x for write speed. The drive is capable of spinning a disc at the required RPM and the pickup assembly is also capable of reading and performing error correction at the read speed of 48x. By unlocking it you are also allowing it to write at the same speed it reads. The only stress difference or quality difference would be the laser assemblies ability to burn the die at high speed. It is either increasing the lasers power output at the outer edge of the disc, or not burning the pits as deep beyond it’s rated speed. Actually, depending on the media and the dye process it may be able to burn the die at a higher speed without increasing the output power due to an efficient dye.
Now going from a 32 to a 40 would still make sense since the 32 reads at 40, but going from the 32 to a 48 could possible be stressing the drive components. If so, then so what? How long did you keep your last cdwriter before you upgraded? If it burns out 3 years from now are you going to be upset when you ditch your 32/10 burner for one with newer features, better compatability and a higher write speed for less than the one you are replacing?
Even if you unlock your 40 to do 48 it will still burn faster at 40 than your 40 would at 40 (higher average write speed) and it won’t decrease your write buffer size like the new firmware does.
I guess the real test here would be to take apart both drives and examine the components.