You try to store a whole stream in one property of an persistent class, that won't work! But the solution is already there,  see this article

Yes, it would

kill
set $p(data,"x",2E6+1)=""
set dynArr=[].%Push(data).%Push(data).%Push(data)
set stream=##class(%Stream.GlobalCharacter).%New()
do dynArr.%ToJSON(stream)
try { set x=dynArr.%ToJSON() } catch e { write e.Name,! }
write stream.Size,!
write $length(data),!

The output is

<MAXSTRING>
6000010
2000000

As Steven Hobbs  wrote, the limit is only set by the size of the (virtual) memory.

It depends on two things,
a) the (user) interface, your user uses and (telnet, web, an application, etc)
b) where your inputs are handled (on server, on users device)
 

The only important thing is,  do they accept data with the arbitrary length. It's not of importance for you, how their API the  incomming data handles: as string, as longstring, as stream, as array of bytes, etc.

So one has a DEFAULT length of 50 and the other 3641144. But I thought more of the difference HOW MANY characters can they hold.

Just a dumb question, what is the very difference between %VarString and %String regarding the storable string length? As far as I know, both have a length limit of 3641144 characters.

I have nothing in common with HealtShare... but a property (Property rsXML As %String), like you mentioned, can hold up to 3.6E6 chars. If your data are longer then 3641144 characters then you definitely need to use streams (and if you intend to Base64 encode the data, then your data will be 33% longer)! You need to change the above property to something like

Property rsXML As %GlobalBinaryStream;

BUT this means, you have to adapt all your programs, methods, etc. where this property is in use!

That won't be a joy rather a pain

Hmm, ... will be difficult, but I give it a try

ClassMethod DNA(dna) As %String
{
	q $tr(dna,"CGAT","GCTA")
}

The spirit of the time... we have to save water, energy, etc. Maybe we should save bytes too...

   // instead of this line
   if (($zabs($a($e(s1,cnt)) - $a($e(s2,cnt))) '= 32)) { return 0 }
   // try this one
   return:$zabs($a(s1,cnt)-$a(s2,cnt))-32 0

That's is easy for the ASCII character set... (you didn't give any restrictions)

ClassMethod CheckOpposite(s1,s2) As %Boolean
{
    q $zb(s1," ",6)=s2
}

what you need is a SIMPLE compare of two strings

Set Ret=RSet.Execute()
set currentTS = $zdt($h,3)    // get onece the current timestamp
 While RSet.Next()
  { Set routeGuid="" 
Set nextScheduled=RSet.GetData(9)
//I $ZDATETIME($h,3,1)>nextScheduled S ^badis("datetime",Id)=$ZDATETIME($h,3,1)_"|"_nextScheduled
if currentTS ] nextScheduled S ^badis("datetime",Id)=currentTS_"|"_nextScheduled
}

In words: if currentTS follows (i.e. greater) nextScheduled - that's all.

If you can't find the methods Vitaliy mentioned because (for example) your Cache version is too old, you can always reinvent the wheel and write your own encoder/decoder method. Where is the problem? This snippet could be a starting point

Parameter Base64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

ClassMethod Base64Enc(x)
{
    s f=-$l(x)#3, x=x_$e($c(0,0),1,f), y=..#Base64, z="" zt:$ziswide(x) "WIDE"
    f i=1:3:$l(x) s a=$a(x,i)*256+$a(x,i+1)*256+$a(x,i+2), c=262144 f j=1:1:4 s z=z_$e(y,a\c+1), a=a#c, c=c\64
    s:f z=$e(z,1,$l(z)-f)_$e("==",1,f) q z
}

I assume, you want to change ALL ..#WhiteSpace chars to the delimiter, used by $piece()

  s $P(replace,",",$L(..#WhiteSpace) + 1)=""

OK, it was a typo and there is nothing to shave 

Some comments...

(1) you can generate a string with the necessary commas, (2) also, the variable "l" is unnecessary and (3) after assigning to "m" the length of the first word, start the for-loop with the next (second) word...

According to problem description, the string will never be empty, so an early "q 0" is also not necessary and for the case, this happens, the first piece of the string will have a length of 0.

Parameter WhiteSpace = {$C(9,10,13,32,160)};

ClassMethod Short(t) As %Integer
{
  s t=$zstrip($TR(t,..#WhiteSpace,$tr($j("",$l(..#WhiteSpace))," ",",")),"<=>",",")
  s m=$L($P(t,","))
  f i=2:1:$L(t,",") {s n=$L($P(t,",",i)) s:n<m m=n}
  q m
}

In case, it's not a typo, tell me the secret of how to "shave symbols" 

You count the alpha-only words, "Let's, 21inc, ..." would't pass the check. So I changed your code to

ClassMethod findShort(s) As %Integer
{
 s s=" "_s_" " f i=1:1 { ret:s?@(".e1"" """_i_"anp1"" "".e") i }
}

I hope, it's OK...

In case, the shortest word is longer then  200 chars, than the result will be wrong. Instead of using a constant (200)

  s l=$L(t,","),m=200
  f i=1:1:l {s n=$L($P(t,",",i)) s:((n>0)&&(n<m)) m=n}

use a more generic approach

  s l=$L(t,","),m=$L($P(t,","))
  f i=2:1:l {s n=$L($P(t,",",i)) s:((n>0)&&(n<m)) m=n}

Also, removing the unnecessary delimiters (commas) simplifies the code too

ClassMethod Short(t) As %Integer
{
  s t=$zstrip($TR(t,$C(9,10,13,32,160),",,,,,"),"<=>",",")
  s m=$L($P(t,","))
  f i=2:1:$l(t,",") {s n=$L($P(t,",",i)) s:n<m m=n}
  q m
}