422h (close to 423) with 84 URs... 5.02?
Crazy, I always thought it was really slow. In fact.. it's only been the last few weeks that I've been unlocking URs like crazy. Last week I unlocked 8 in about 3 mil credits. I've found that at a certain point when your manifest is "good enough" (with some URs mid to high level) you can really start saving up cash and then blowing it all at once. This will maximise time in game and earning credits, and less time wasted going to the store post match.
I've still got a long ways to go to max out my manifest, but my recommendation to anyone starting out (or even mid way through maxing their manifest excluding URs) is to buy recruit packs to max commons, then vet packs to max uncommons, then spectre packs to max rares and especially gear. Once your gear is maxed, you'll definitely think you're seeing a LOT of URs in your psp's, which can help you make that continued push to the end.
Just my experience, no hard numbers.. but damn. I've been hating the fact I didn't have the harrier until Retaliation, but when I unlocked it and maxed out my gear, I just started unlocking lots of URs.