Just a thought...
The 030 combo has 4 megs onboard without any simms (at least mine does!) I suspect the 4 meg expansion card is cancelling out the 4 megs on the combo card, leaving the 2 megs on the 2091. You're only allowed 8 megs of fastram.
When the ram conflict is resolved, the combo should run at proper speed (leaving out the 2091 scsi card would do it and leave a nice 8 megs of fastram)
Or possibly the two scsi cards are conflicting? Either way, leave out that 2091 and I figure problem solved.
Why do you need a 2091 scsi card with a GVP 030 combo? It has scsi onboard. That's the point, right?
Maybe I'm missing something....
Anyway, hope you get it solved.