The GT 630 Rev. 2 is certainly a very interesting card for several reasons. The only other Rev. 2 in the present lineup is the GT640 Rev 2, but that has a 49W TDP and is also a 384 shader card.

As well as the 25W TDP (which in theory only would make it the best performer/watt, perhaps a bit like the GT240's and similar was when they first came out) two things stand out; it's single slot width and does not use a GPU fan (it's silent).
Single slot means that if you could get a motherboard with say 7 PCIE slots (that are actually usable) you might be able to build a reasonably powerful yet inexpensive system.
Typically, the small fans on small GPU's are very poor (they often fail and sometimes don't even cool well). On a 25W GPU you shouldn't actually need them and it would be better to have good system cooling. Just blasting them with 2 or 3 large fans would keep them cooler than small GPU fans.

If the 692.7 GFLOPS is even close to the mark for actual relative performance here then even 4 of these (2770GFlops) would outperform a GTX670 (2460GFlops). The problem is comparing the 692.7 vs GFlops of mid range to high end card is probably way out because there are several serious issues with these little cards. The bus is 64bit and the bandwidth is 14.4 GB/s. That's almost Off!
Even the GT640 Rev.2 has a bandwidth of 40 GB/s, which might-well actually make it the better choice for here. Just how such bandwidth and bus restrictions manifest themselves when it comes to performance is the question. The way I see it is there are 6 cards in the 600 series with 384shader cards, but the performance will be all over the place for different apps - some are DDR3, some DDR5 (frequency from 1800 to 5010MHz), some are PCIE2 X8, others PCIe 3.0 x16, the core clocks range from 810MHz to 1046MHz, buses of 64 or 128bits and bandwidth from 14.4GB/s to 80GB/s. On top of that these small GPU's may not stand the test of time when it comes to crunching here and unless these could return a WU inside 24h (highly unlikely) it would be difficult to match the credit of bigger cards. They should finish inside 2days however.
You would really need to test all 6 384CudaCore cards performances here to get real measurements and work out if their performances/Watt and performance/purchase cost actually makes them good cards or not.
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I've got a GT640 working here, standard 900 / 1800 MHz memory clock and chip OC'ed to ~1.1 GHz. The memory controler is already at 66% load running CPU-Grid. Imagine how badly crippled a card with about the same raw horsepower and half the bandwidth would be! I think that's why they can put the TDP so low: with such a low bandwidth it's just impossible to feed the GPU properly, hence it won't consume as much electricity. That's not exactly efficient from my point of view.

What I think of this card:
- performance likely really bad at GPU-Grid (Einstein would be even worse, POEM would be totally fine.. it really depends on the app)
- actual power savings not that great, even if performance is not crippled by bandwidth: the regular GT640 uses nowhere near its TDP either
- you "loose" one CPU core to support each of these
- won't age well at GPU-Grid, will be the 1st Kepler to miss the bonus
- if you have one it's probably better to run something else on it
- don't buy one or many for GPU-Grid

MrS
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Scanning for our furry friends since Jan 2002