Seriously, I would recommend you to get 5 pieces of these Twinfury-USB-miners at a very recommendable price :
http://minecoin.net/shop/Bringing them to 3ghs is quite easy. I have pencil-modded all my red furies. 8 of them run on about 3ghs and only two run on 2.7-2.8
Please tell me more about the pencil you used. I've got some red/twins running atm but none is willing to get faster than 2.7 GH/s.