Nokia lumia 925 vs Lumia 630

If you are on T-MoUS, they seem to be putting 925 out to pasture. No guarantees it will advance beyond Cyan.

In general, 925 has a better screen, better CPU chipset, more RAM and better camera. Future vs Spec?

The 925 is still a great all around Windows Phone. If you aren't worried about latest and greatest, why not give 925 a home...
 
Given your short list, I think it's quite clear you should go for the 925: 1GB RAM is good for games, and the 8.6 megapixel OIS camera easily outperforms the 5 megapixel one on the 630.

However, there are things you won't get on the S4 powered devices like miracast support.

As for lag, Windows Phones don't generally lag the way Android ones do. Even a low end device like the 630 is smooth by comparison with dorids and MUCH more secure.