The SM7b is a really great mic as well. I use it with my grace 101 usually.
I don't know much about the speck mic pre..
But the sm7 is a really warm and some would even say it's slightly dirty. I would say warm, not the later though. I use it with the grace 101 because the grace is a really really clean pre and it almost balances out the warmth really well. Or at least, it certainly doesn't make it any warmer really.
I don't really know what the speck is like tonality wise, but if you are considering the sm7b, you may want to consider what type of sound you want to go for..
Every one is recommending a lot of pre's. And from what I've read or know personally about the pre's is that they're all great. But make sure that these pre's and mics you're checking out, are best suited for what YOU want to do. If you want a great vocal mic, SM7 = yum. If you want a versatile but still really good vocal mic, you may want to go back to your AT that you were originally thinking about.
For the most part, all (and I really mean all) mics, and all (and I still really mean all) preamps can be great, but make sure that their sound qualities and characteristics match what you're going for.
Hope this helps.