Cable Modem Placement: Longer Ethernet/Shorter Coax vs Shorter Ethernet/Longer Coax
I think your configuration (despite the apparent confusion in some earlier comments) is: coax to cable modem, then CAT6 from cable modem to a router, then CAT6 from router to point of use.

RG6 coax, which is used by CATV systems, has an attenuation of ~ 6dB per 100ft (@ 1000MHz). CAT6 has an attenuation of about 9dB per 100ft (@ 200MHz). All other things being equal, coax will suffer less attenuation of relevant signals. 

However, the signal strength margin (how much stronger than the minimum acceptable input for your cable modem) your CATV signal has when it enters your house is unknown, and could conceivably be just enough for your present 50 ft coax run, so that adding an additional 30ft to it could push your cable modem "over the edge". The Ethernet signal is starting at a known strength coming out of your router, and has enough margin to travel 100m (as long as you use good quality CAT6 and connector terminations), so the 40-50 ft you need is well within published expectations.

All said, I think Option 1 is slightly lower risk. but make sure your Ethernet cable, patch panel, and connectors are high quality, or you may compromise the published 100m range dramatically.