I'm pretty sure the envelope is the same length (or very close), but the GE envelopes do have a larger diameter, so their volume appears to be greater. The same is true of the standard GE lamps in a store, so I'm wondering if it has to do with their manufacturing process.
The filament heats up immediately regardless of the capsule diameter. The smaller the capsule, the faster the capsule reaches the critical temperature threshold for the halogen cycle to begin. But that doesn't necessarily mean a bulb with a small capsule is better than one with a large capsule.