Even with the large aux tank a Challenger 850/CRJ2 won't be anywhere close to touching the range of a Global Express or G450/550. Those planes have 12+ hours of endurance in the mid to upper-40s.

Doing BED-VNY or LGW-TEB in the winter, however, should be within the 850s range and ability...especially if you climb it above 370 (which should be no problem on a 4+ hour segment).