Yes, to get such quick replies it seems to be the case, great

Good to know. So your drive takes like, say 5:30 minutes or so to burn a whole dvd, right? That would be +- 18x speed typical. Just to be sure we are all talking about the same here because as I said, my drive also says it does the burn at 18x, and produces readable dvd without problems, only that it takes much much longer, so that the final REAL speed is about 6x....
Could you do me a favor and make your next burn with growisofs or k3b? or even cdrecord/wodim whatever? To see if it takes the same time... then at least I can be sure that nor those burn programs nor the drive itself are causing the slowdown, in that case it would be my pc. But if you do get slower speed with growisofs et al, then it would be a bug in those programs or something...

Because, the problem is that I've already tried everything...
but for your all information, here it goes:
I have Mandriva 2006 with custom 2.6.18.1 kernel working fine, my hardware is not the newest but has decent speed (AMD Athlon XP1500) my drives are EIDE, harddisks on first channel, dvd is single master on second channel.
I have DMA working (did a readcd which gave me about 16000kB/s, and my harddisks are giving me (output of hdparm -tT) about 46MB/s). dvd drive is in udma4.
I can burn cds at full speed, and everything else seems fine, except for the fact that burning dvds seems to happen at 6x speed, and apparently not due to system slowdown, but to using wrong speed...

running growisofs at the command line (or over k3b, doesn't matter, i've tried both) starts the burn saying speed is set at 18x, but then the values reported in the meantime go around 5 to 7x and at the end it says: average write speed: 6.1x or something like that.
If I run wodim it doesn't even want to start with more than 6x...

Funny thing is I pretty much know why all this happens, just don't know what to do against it and what is causing this: dvd+rw-mediainfo reports 6x as current write speed if I have a dvd+r in the drive (with both sony 16x and verbatim 16x), although in the list of write strategies correctly appears all speeds up until 18x!
So I think that's why it only burns with 6x... wodim -prcap also reports current write speed 6x (=48x cd). Actually that indication is something that bothers me! Because as we know, 48x is drive's max cd speed... could it be a bug in those tools or kernel or whatever, causing them to set the drives' max speed at its max cd speed, 48x, which equivals to 6x dvd speed?! Because yes, the drive does have proper writing strategies with those medias, just had a look at the firmware excerpts here on another thread in the forum. Also just did a boot with win, quickly installed nero from some disc lying around here and did a test burn, it said burn speed to be 16x, and finished 2100MB in 3,5 minutes, which seems pretty decent to me... so it's not hardware nor drive or media... now I'd really like to find out what is wrong then... because if there is one thing I do NOT want to do is start burning with nero for linux... I think, being this the linux area here, I don't have to explain why, no?
(Though I might do it for testing purpose, to see if it then reaches max speed... this at least would help me to isolate the cause).

So, any comments or ideas are much appreciated. Let's get to the bottom of this! (because I did a little search on google, and seems there are quite a few people having the same issue...).