Hey Phil, had a listen to v4, didn't think it was too bright. I think you are pretty close to your reference and i'm pretty familiar with most of what carcass has ever done. Funnily enough i was just listening to carcass and napalm death minutes before listening to your song, after commenting in another thread.
The kick drum sounded more roomy and less close miked than the carcass tracks i just listened to, a bit boomier, less clicky if you know what i mean. I didn't mind the sound of it, it just sounded a bit different to what i'm used to in that style. The rhythm guitars didn't seem to have the 'body' and depth, or balls and guts of the carcass tracks i listened to, and in retrospect maybe they were just a tad bright or a bit fizzy by comparison. Sounded a bit closer to bolt thrower than carcass in parts. Lead guitars sounded right to me though, tone and playing wise. Wasn't trying to compare you to carcass, i think the sound of your mix stood up fine in it's own right, just my take on your reference.
Pretty good job so far - haven't listened to much stuff like this for a while though.