I have always assumed that the XL means Extra Long. This disc places at 8K on the MST Flight guide making it a little bit on the slower side and slightly understable. Sounds like you could use this disc!
XL by Discraft

PDGA Official Specifications
Diameter:
21.1 cm
Height:
2.1 cm
Rim Depth:
1.2 cm
Rim Width:
1.7 cm
Max Weight:
175.1 g
Date Approved:
Apr 3, 1998
Who is the manufacturer?
The ESP XL is made by Discraft.
What is the disc model?
This is the XL. Check it out on our famous Flight Guide! You can also check out more XL discs here.
What type of disc is this?
This disc is a Control Driver.
What are the flight numbers for this disc?
The flight numbers are 7 / 4 / -2 / 1. Flight numbers are displayed as Speed / Glide / Turn / Fade. You can compare this disc on our Flight Guide too.