The main difference is in the chipset used. The 945 chipset is effectively an old 800FSB chipset pre-overclocked to run at 1066FSB and to make it stable they sacrificed the PCI and PCIe locks. You won't get anything over 300FSB on the ASRock, ever. So, you'll be stuck at 2.1GHz, but it is a rock solid, fully featured board with SATA RAID, IEEE1394, good sound.
For about £35 more you can get the latest chipset, the 965. It will clock as well as anything else at the moment, but you need good RAM to go with it as it lacks a divider. Most E6300's will hit 400FSB without any extra voltage, so you are looking at 2.8GHz as long as you buy PC6400 (DDR800) RAM. At the moment, 2Gb Geil Low Latency PC6400 RAM is on special offer at £165, which is a real bargain in anyone's books.
The choice you have is whether to buy the ASRock, E6300 and PC5300 RAM or the DS3, E6300 and PC6400 RAM.
As there is no price differnce, I would buy the PC6400 RAM anyway. It will survive at least one more upgrade than the PC5300 RAM.
Then, I would ask myself very carefully if I really want to pass up the chance to have an extra 700MHz of processing for an extra £35. I, personally, think it's a no-brainer, but you may disagree.
If you buy the Gigabyte board, the E6300 and the Geil PC6400 RAM I would be prepared to guarantee that by following the instructions in the DS3 sticky, you will hit 2.8GHz without adjusting the voltages. That means you cannot really damage the CPU as you can't overheat it or over-volt it. The worst that will happen is that you have to reset the BIOS. As the RAM is reputed to be good to at least FSB1066, you are then looking at how far the CPU can be pushed, but you can leave that for when you feel the machine is slowing down a bit
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You won't regret buying either board, but the Gigabyte can be easily overclocked for a very large amount of free extra performance.
