GVP HC+8 SCSI+RAM Board - upgrade options

[Ilwrath]

Yikes!  You put this card in a 4000, and it worked??  
The GVP Impact series were 16 bit controllers, with 16 bit RAM.  The controller will be reasonably fast on a 4000, but the ram is going to be REALLY SLOW.  (Like designed for a 7mhz 68000, slow...)

It's a Zorro 2 card, and the details for it are listed at Amiga-hardware.com:  GVP Impact Series II 2000 HC+8

There's all the jumpers, but being a 16bit card, you're maxed at 8mb RAM on it.  Sounds like it's already full.  As for the half-sized SIMM modules, later of the 32-pin SIMMS were much smaller than the early ones.  It probably originally had 4 mb on it, and someone upgraded it to 8mb, later.

[Ilwrath]

Well, what would be really useful would be a fully documented spec sheet of the A4K, so I'd know its internal/external full capabilities... Any good link on that ?

Yes, as a matter of fact, Warren Block's Amiga 4000 reference has proven it's immense value to me quite a few times.
Amiga 4000 Hardware Guide 4.2

As for the GVP HC+8, the SCSI controller shouldn't be overly slow.  I'd imagine 1-3MB/sec sustained.  About all the early SCSI HD's could do, anyhow.  I'd expect it to perform adequately for CD ROM and HD access (though not really a speed benefit over the on-board IDE - but SCSI CDs are much more reliable than ATAPI CDs on the Amiga's IDE chain.)

The RAM on board that card will be much slower than RAM on the motherboard of the machine.  (Which, in turn, is much slower than RAM on a dedicated accelerator card in an A4000 -- the person that told you the RAM on the GVP would be fastest may have thought you had a GVP accelerator card, instead of the HC+8 card)  If you choose to keep the card in your system, I'd make sure to set that as the last available RAM to the machine.

The GVP Impact series 2 cards were the cream of the crop for the Amiga 500/2000 computers, but the memory speed, especially, is lacking for the Zorro 3 based machines, like the A3000 and A4000.  

The maximum motherboard FastRAM is 16MB on the A4000.  Other choices for adding faster RAM and/or  SCSI to an A4000 include the FastLane Z3 SCSI by Phase5, and the C=4091 (though it has no options for additional FastRAM)  And, of course, the fastest is if you can pick up for cheap a CyberStorm or WarpEngine A4000 accelerator card.  (I have the old-style CS MK2 in my A4000, and I still remember how amazed I was with the speed increase of having a processor card with the FastRAM available sitting a half-inch or so away.)  Plus, most have either built in, or an optional module for a fast SCSI II controller.