The pressurization control system is different, no dual CPAM.
No flaps 8. Some CL65s didn't have it either for a while.
The fuel system is different. Forward and aft center tanks as well as a tail tank. 19600lbs depending on how you fuel it.
ECS is different. It actually works
No wipers
EICAS doesn't show as many systems. Not sure if they have improved it on the 850.
Obviously all of the weights are different as well as the shorter wing and fuselage.
Since they go international a Challenger will have significantly more avionics equipment, IRS, HF, dual CDUs, etc. than a typical CL65.
In reality a 604 and a CR2 are similar in much the same way a CR2 and CR7/9 are similar. The manufacturer just chose to certify it as a CL60 instead of a CL65. The CL60 flies like a CL65 on crack.
Personally I'm glad they did it that way because it protects the jobs of the contract/corporate guys. There are just too many operators that will bargain down to the lowest price (a la Legacy) for contract flying to have meat in the seat.
Any Challenger operator with a brain is going to see value in your CL65 experience but corporate is as almost as much about your personality as it is your experience. Show up with the right attitude, make sure it's someone you want to fly with, and if they like you they'll send you to school. In 121 flying you're only stuck flying with a jerk for 4 days, corporate you could be stuck with a jerk for years.
If you're talking about a 601 the basic systems are similar but there isn't as much automation. Of course that depends on if you are talking about a -1A, -3A, -3A/ER, or -3R. Several of the schools have offered 601/604 differences and one offers 604/CL65 transition but they don't go the other way. They'll offer classes based on what the market will bear.