Originally Posted by ericm979

I have not ridden Ventoux but I have ridden and raced many similar (or even more difficult) climbs.

Use the road bike. Put appropriate gearing on it. Merlin's suggestion of testing on a 10% grade is good but then you need to remember that you'll be doing a long climb and it'll be at altitude. It's also often windy on Ventoux, and head winds make climbing harder. So you want a lower gear than you find comfortable on a short 10% climb.

I strongly recommend a 50/34 "compact" crank. Since you are inexperienced with big climbs and say that you're not fit, I suggest relatively low gearing, such as a 12-34 cassette. You will need a 9sp MTB derailleur (Shimano) or Apex long cage (Sram) to shift it. A 9sp Shimano derailleur works with their 10sp road shifters.

Practice eating and drinking while climbing. You can't wait until you get to the top.