But I still need to know if it would be better to just buy another 50 feet and a connector, or just get 100 feet of the same stuff. I have 50' of RG-8X and it works perfectly.
I'd suggest 100 feet of the same stuff, but it's up to you if you want 50 feet, a connector, and another 50 feet. I don't have much experience with that much coax, but the loss is probably close in either case. You're talking 100 feet of coax which will have loss most likely due to 1) length and 2) Shield, and in the other case, loss from the connector and two coax cables.
Dave or sean may be able to provide more insight...
Jason
P.S. Isn't RG-6 75 Ohm coax, not 50 Ohm? I'd prefer the RG-8 over the RG-6 if that was the case. I'm too tired to look it up at the moment (just got back from a concert).