As with almost any question related to computing performance, the answer is: "it depends". For all practical purposes however, the 925 will be faster at almost everything.
The quad core in the 630 is for marketing purposes only. The integrated CPU has four cores, which for the first time are not krait cores. These are the worst performing cores ever used in a WP8 device to date. The only scenario in which the 630 could theoretically perform better is when running apps that use more than two cores. I'm not aware of a single app on WP that uses more than two cores. Even if such an app did exist, excessive throttling would ensue as soon as the app decided to exercise more than two cores for any notable amount of time, eliminating most of the theoretical benefits (to remain within CPU power and thermal limits).
If you are worried about loading/resuming time, you'll want:
- to avoid closing apps (so apps that you've opened stay open)
- fast cores (because app-loading only ever runs on a single core, so fewer but faster cores is much better than having more cores that are slower)
- lots of memory (increasing the likelihood that a previously launched app will still be in memory, which will avoid app-loading entirely)
For all of the above, the L925 is better.
The only two devices that exhibit better performance than a L925/L920 are the L1520 and L930/Icon, but the differences aren't as big as the numbers on paper would have us believe.