I just bought a Gregory 80L backpack, will this bag fit in the bag compartment located at the bottom of the pack or should I keep looking for a down bag that will fit my 6' 8" frame?

Tech Specs:

Material:

100% Silky taffeta nylon 

Insulation:

Climashield HL 

Shape:

Mummy 

Max User Height:

[Reg] 6ft 4in (192cm); [Lng] 6ft 8in (203cm) 

Shoulder / Hip / Foot Circumference:

[Reg] 66 / 60 / 42in (168 / 152 / 107cm); [Lng] 68 / 60 / 42in (173 / 152 / 107cm) 

Stuff Size:

11 x 21in (28 x 53cm) 

Stuff or Storage sack:

Both 

Weight:

62oz (1628g) 

Warranty:

Lifetime 

Degree:

20F / -7C 

Recommended Use:

3-Season backpacking and camping