Depending on the price that you are getting the 8x drive for, this would be the factor to make the decision. You are going to get the same quality, you will just have a more reliable burn witht he newer technology and it will be up to date.
The Plextor 8432 was a solid drive. I have not seen a big difference betweeen that drive and the newer faster drives, but the new 12x and 16x plextor drives do have the "Burn Proof" Technology. You can read about this at
http://www.plextor.com/english/products/16_10_40A.html
Hope this helps with your decisions.
Thanks,