Hi,
I found an MSI H77 model and it seems pretty good. Also, it fits into your budget quite well. The model is MSI H77MA-G43. IT has the 4 ddr3 slots that you are looking for. Also, it is the same micro atx size as your asrock one. Finally, the MSi comes with OC Genie which means you can easily overclock. This is a great software and you will be missing out on this if you buy AsRock. The price for this one is about £65. Here is a link : http://www.amazon.co.uk/MSI-H77MA-G43-Motherboard-LGA1155-Micro-ATX/dp/B007KZQFES/ref=sr_1_2?ie=UTF8&qid=1382386436&sr=8-2&keywords=h77+board. There is also an ASUS H77 board with the features you are looking for. It is the ASUS P8H77-M board. This is also a mATX size and has the 4 dimm slots. Also, ASUS is the leader in boards due to their reliability and quality therefore this will also be a great choice. Also, the ASUS comes with AI Suite which is a great software that allows for easy over clocking, fan control and system monitoring. I myself have an ASUS board and I am extremely happy with it. The board costs £65 as well. Here is a link:
http://www.amazon.co.uk/P8H77-M-Motherboard-Support-Express-CrossfireX/dp/B007KZQERQ/ref=sr_1_8?ie=UTF8&qid=1382386712&sr=8-8&keywords=z77+matx
Otherwise, why don't you go for a Z77 chipset. It is way better than H77 and you have way more options for boards. A good option is the AsRock Z77 Pro4-M board. Again this is mATX and has the 4 ram slots. Also since it has the z77 chipset which is great. This board is also very good quality because it is the pro-4 series and therefore you should be happy with it. The only thing you may miss with AsRock is software. ASUS and MSi have far better softeare than AsRock. Anyway, there are also many other options. This board costs £67 and here is a link:
http://www.amazon.co.uk/ASRock-Z77-Motherboard-Instant-Charger/dp/B007RS70YW/ref=sr_1_1?ie=UTF8&qid=1382386900&sr=8-1&keywords=z77+matx
Hope this helps!!
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