GSA-H42N reads some DVDs real slow

I am seeking knowledge for my GSA-H42N.

It works fine, but when using to copy unprotected DVDs to my harddisk it is really slow. It starts with ~2800 kb/second and goes uo very slow.
I repeat: the original DVD is not CSS protected, its not a CSS-issue!

This does only happen from original DVDs. The same copy is read pretty fast. its starts with ~8000 kb/second and goes up pretty fast.

I tried all the following firmware combinations:
) original RL00
) original RL01
) MCSE*-modified** RL01
) original RJ11 (Buffalo)
) MCSE-modified RJ11

*MCSE V1.1.0.12
** modified= increased read speed & RPC1 patch

No change.
All firmwares do their job (reading and writing).
I have not found ala42s modified firmware anywhere on the internet (all available links where broken).

Can anyone enlighten me:
) why does the drive read the original disc this slow? The firmware is MCSE-patched and should allow faster reading.
) Can you recommend a firmware: RL01 or RJ11. It seems that RJ11 follows newer specifications from LG so it seems wise to use it. On the other hand it is not an official firmware for the H42N.
) Others have problems with CD-burning. I have not yet burned a CD with this writer. Is it recommended to flash it to H44N like described here?

Yes, I have searched through tons of threads but no thread did really enlighten me. Maybe its my fault so I would really be thankfull for your help.

Thx,
Makumba

PS: All ripping was done with DVD Shrink 3.2.0.15. I want to reauthor a disc.
The same original DVD is read at fast speed (beginning with ~7800 kb/second) with another DVD-writer on the same PC: NEC ND 3570A. So its for sure nor problem with the DVD.