indysmith,
As you know, I've got the same amp as you, a 4104 800 combo, I found out not long after I bought mine that one speaker wasn't working, so I had to replace it. I've had a V30 loaded combo before, and they do sound sweet, so I went for one, and as I had it serviced at the shop I bought it from, I got it cheap.
The OEM speakers G12M-70's aren't made anymore, the closest is the G12T-75 found in most 4x12 cabs etc IMO don't sound that sweet, where V30's have supposedly been engineered for a better tone and what have you. I like 'em anyway, and most large amp companies fit 'em as standard equipment I believe (MESA/ENGL/some Marshall...)