Urgent Which RAM Question - Help!

[hitman]

I recently built a system using overclockers and advice from the forum. I've built the machine using the following RAM :
Patriot Sector 5 Viper II 4GB (2x2GB) PC3-12800 1600MHz Dual Channel + 3D Mark Vantage (PVV34G1600LLKB) £80.99

My motherboard is a gigabyte GA-MA785GT-UD3H

The problem is I now need to buy 4GB more but overclockers is out of stock and recommended I go for another make instead. Is this ok to do? If so which should I go for?

I need this quite urgently to get som software to run properly so any advice most appreciated

 

[hyperst]

its generally considered best not to mix ram

 

[hitman]

OK, I might buy 8 GB of completely new RAM then and sell the patriot ram on ebay.
Can anyone recommend me some ram?
cheers