It's actually a good question - the specs are:
F** J: 1.5" width at nut, with 9.5" (241mm) radius;
EBMM Sterling 4: 1.5" width at nut but with 11" (279mm) radius
"The radius quoted in the specification of a string instrument is the radius of curvature of the fingerboard at the head nut." Radius is a definitive measure that doesn't have as much to do with neck comfort as "neck shape" which is fuzzier and not often quantified.
Go play each instrument in turn and determine which feels more comfortable. Radius won't explain the difference between, say the F** Geddy Lee, which has a "thin C shape" and the F** Am Standard - both have the same radius, yet everyone will note the G.L. has a thinner neck.
But to answer the OP's original question, I find them "roughly" similar - certainly more so than, say, a F*** J and a Bongo (1-5/8" (41.3 mm) width at neck, 279mm radius), or a F*** J and a F** P (1.625" (41.3 mm) wide, 'modern C'). Then of course there's neck taper, etc. I find the J neck thinner than the Sterling; the G.L J is "stupid thin" in my opinion - it gives the illusion of being "faster."