Seems that I have to finish building my 534 with these nice figures
So far the 534 has more than exceeded my expectations

It's running stable at 40Mhz with anything I've thrown at it so far. The CPU is rated for 33Mhz but it's not really getting that hot so I will try with 50Mhz this evening.
The only real issues I have left now are:
- uIP with NetUsbee is not working when I run @ 40Mhz (only at 8Mhz - but emutos does not boot at that speed if I have FastRAM enabled)
- the IDE port on my blitter board is the same. It works only if I run the TF @ 8Mhz.
I really don't care about the IDE port on my blitter board now that I have the Terriblefire (I'm going to make a version of my blitter-board with a Ricoh realtime clock instead) - but I do use the NetUsbee for transferring files between PC<->Atari and would like to get that working at least.
However, looking at the source for EmuTos and uIP I think the issues might be related - they both perform some kind of speed tests to figure out how much delay they need to put in between various operations. My gut feeling is that this is what is causing the issues but I am not 100% sure.
Of course, the speed when going through the ST bus is held back to pretty much stock speeds so if it thinks that we're good to go for 40Mhz all the time then these delays will end up being off...
Also, the Terriblefire IDE is not working for me in Tos2.06. Not really bothered about that but I will at least try hooking up the IRQ line and see if that solves it.
I made a github account, and will spend some time reading up on how to use it. I want to make a proper pull request for my changes to go into the official firmware.