PS: I never went to C OR C# so maybe 50-110 but my guess their going to be stiff and put a lot of tension on neck when tuned to E or Eb
Oh, you'd be surprised.
There are a number of reasons why 110 is the largest commonly-used 4th string in sets (and significantly less so than 105, at that). Tradition/habit, comfort, tone, inharmonicity.
However, tension on the neck is *not* one of them.
Take for example the D string in standard tuning: many players use a 060 for it. Do you know how thick a string must be to match the tension of a 060 D, but be tuned an octave lower? The math (assuming proportionally constructed innards, only scaled up - which isn't necessarily true, but never far from the truth either) is simple: it needs to be double the diameter of the octave-up D, i.e. 120. Yep, that's right: any string thinner than 120, tuned to low D, has less tension than a bog-standard 060 "high" D, a gauge which countless of us have used many times, never once wondering whether the neck could withstand its tension.
Now, perhaps even more players actually use a 065 for their 2nd string. Want to know how thick a string must be in order to have the same tension at octave-down D? Same principle: it must have double the gauge - in other words, a 130. Yup. One can - even though few do - use a 125 low D, and not reach the same tension of one high-D gauge that thousands of players use every day without a second thought.
I could go on. Personally I've never tried it, nor do I have any desire to, but both Ernie Ball and D'Addario have a 50-70-85-105 set in almost all of their product lines. You know by now what I'm getting at: if one uses a 070 high D, their neck has nothing to fear from a whopping
140 low D.
Finally, let's take a hypothetical Steve Harris fan, who uses Steve's signature bass (essentially, a P bass with a baseball-bat neck) and signature string set. If they - and said neck - can cope with a Rotosound flatwound 075 as their high D, by the same token they could a 150-gauge low D, because anything smaller, no matter how subjectively huge, will nonetheless have
less tension than that 075.
Again, there are more than valid reasons not to pick these bridge-cabley gauges. Just know that the neck would be fine even if you did.
And sure, picking gauges so that
all four strings have the same, high tension may well end up being really taxing on a neck; however, nothing would prevent one from using a gigantic low D but low-tension high strings, making the total pull (which is the only thing that matters to the neck, unless tension is so asymmetrical that it twists it) a wash. Why you would want that, and end up with a very poorly-balanced set, tone-wise) is another matter. But you definitely could, and the neck would be perfectly safe.