Easy solution: 3 HDL on the same memory card
Well, I may not be the right one to answer but I'll try to do my best.
Actually I don't remember if the default speed is already the highest speed the PS2 can handle. I don't think you can increase it too much any way.
You should try to raise the speed and see if everything's fine.
According to rivaldinho an UDMA 133mb/s HDL07c version works (but I don't know anything about which games are compatible).
Actually I don't even know which is the default DMA :P
As I said in the first port, I'm more or less a newby just trying to share the few information I've found.
Since to have a UDMA (or MDMA) version we need to patch the original HDLoader, I cannot answer and I can only say the default DMA is not UDMA nor MDMA, sorry.
Maybe this thread will be seen by an expert who want to answer (none of my PM to some of them had any answer till now...)
This "slow trash" is VERY useful.
I'm using the MDMA version to play SC3 since using the original DVD takes FOREVER to load every battle (and since every battle is 10-15 seconds long, you would spend more time waiting than playing)!
Anyway someone told that they cannot become modes within the select menu due to problem of "space" in the core code and because when the software (HDL) starts it has already told the HD how to behave (which DMA to use) and it cannot tell it to change DMA mode on the fly (that's why they cannot become modes in the select menu).
Anyway if your smart you can simple put 3 HDL07c version on the same memory card and use any launcher to use the one you want.
I have a x-port (MaxDrive can be used as well as all the other ways to transfer files on the memory card) so I use SaveBuilder to make a home made game save called HDL (this is actually the name of the folder) in which I put a 07c standard version (more speed), a UDMA0 version and the MDMA0 one (more compatibility, less speed).
I upload the save on the memory together with another save for the exploit (using any launcher as BOOT.ELF) and configure the launcher to launch with one button the 07c standard, and others to launch the UDMA and MDMA version.
So there'is no need for new modes within the select menu (just some available space on the memory card ;P) since this way you can have the same feature without the need of newer patches ;)
It may be useful to use the GUI to patch the HDL to change the splash and background images with a completely black image to save space (in this way all the three version fit less than 600 Kb!)