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You can't have the same error if you have allocated 7gb of ram. Giving it that amount of ram is not going to help and could give you worse performance.
Create your own thread and post your own log.
To all the people just posting that they have the same error, please don't, because you may not have the same error. Post your own topic and your own logs. @R3N3 please post a new log.
Try not using java 8 as it broke the old packs. You could also try the beta launcher.
Follow the guide linked below.
http://support.feed-the-beast.com/t/basic-troubleshooting-guide/39
If you tried to run the 1.6 packs with only 1gb of ram you would have most likely got a similar error.
I was helping people when the 1.6 packs arrived and saw lots of threads with memory issues because of people still using a 32 bit os and/or 32 bit java.
Use mcedit and delete the quarry located on line #11 of your log.
I know you said you did not want to lose the world but the pack is in beta and you may lose the world in a future update.
Also take regular backups of the world.
The java 8 update 20 broke the 1.5 and 1.6 packs and I think does the same to the 1.7.10 ones. So if you want to use java 8 then remove you current version and use one prior to update 20 or java 7.
I think that redstone engines don't work with the pump now. Try a different engine to see if that works. A TE engine will work just use conduit to connect to the machine.
Look at the link below for help. It is for the Unleashed pack but worked for me when I had the same issue with a 1.6.4 pack.
http://www.reddit.com/r/feedthebeast/comments/267rxk/help_unleashed_nei_displaying_00_pages_wiki/
I don't know much about linux but should you not be using java 7 and not 6.
If they are are specific forestry saplings then they maybe do not work in anything but a forestry farm. The vanilla saplings should work fine.