The GVP is a SCSI-II device (a lot faster). A2091 is SCSI "1" (slow).
Even the first GVP ROM accepts 1Gb HD, the pretty same as the 6.6 ROM of the A2091.
If you want to keep both (memory expansion?), use the 2091 as a HD holder (move the boot jumper to disable) and just use the image of the 7.0 ROM into the expansion drawer of Workbench. This way you use pretty much any HD you want on it (the 2091) and boot from the GVP one (just the boot HD and a CD-ROM, for example).
[EDIT] The 1.0 ROM on the GVP SCSI 8+ (not the HC series!!!) only allow disks up to 100Mb(!). Grab an upgrade ASAP! That controller is way better than the el-cheapo A2091.