I have some suggestion for the hud/gui.
Show total damage reduction provided (on the armor piece) instead of a percentage of 0-100 per piece. Its a bit confusing when you dont see actual values.
This way you can actually see how much defense each piece of armor gives to you and then add them all to calculate total damage reduction.
If we follow MC standards, armor can only provide 80% reduction, not bad for vanilla, not really enough for modded.
GTExtras should be able to provide 100% if all parts are maxed (this would include a massive overweight/absurd energy consumption of course).
Also following MC standards each armor piece should yield a different maximum percentage damage reduction.
Helmets would provide up to 15% of total reduction (the GUI would display a 0-15% value on reduction, for example).
Chestplates would provide up to 40% of total reduction.
Leggings would provide up to 30% of total reduction.
Boots would provide up to 15% of total reduction.
Now for other things:
Weight excess reduce speed proportionally. (1000 max weight = 100% speed, 1100 weight = 90% speed, 2000 max weight = 0% speed)
Speed reduction/acceleration would be shown on GUI as pluses or minuses, to denote how each part is affecting your speed, just like armor.
Tanks would show total time underwater (or affected by a potion type) available.