Can you foresee any obvious gameplay/balance problems if I were to houserule save rolls to succeed on 5+, like attack rolls do? I want to experiment with a mechanic where, if you do the +/-2 hull points for +/-2 movement trade, the weight of your Mek affects your chance to dodge. This makes sense to me, since if your Mek is loaded down with extra armor, it won't be as agile and conversely, if you strip off a lot of armor, you should be more mobile.
I suppose it could still work with saves at 6+, but then heavier Meks would have zero chance to save, which I don't think would be fun. I want to give them SOME chance, however slim, to dodge.