I have some more q.o.l. mods in mind that compliment the G-R-E-G-T-E-C-H experience but do not add any items or blocks:
Summary
Journeymap to put down waypoints and have a world map drawn for you as you explore.
Waila and Waila Harvestability to get a little info about the block or machine you are looking at.
Prosperctors Journal writes down any ore bearing rocks you find in a digital journal so you can come back to mine the ores later.
GT6 NEI Ore Plugin adds tabs to NEI which display info about ore veins that gregtech 6 generates.
FastCraft improves MC performance.
Fullscreen Windowed makes playing 1.7.10 in fullscreen enjoyable.
Not Enough Items more like too many items o_o
There are probably more miscellaneous mods that can be added in your GT6 pack but these are the ones i use.