Hey thejugador and welcome!
Good to have you around, thanks for your post!
As Alan mentioned,
Equilab Omaha is
the best place to start, here you can create scenarios to calculate how certain hands and ranges perform against others.
The percentage an A high and straight flush will win is very high of course, as the absolute hand strength is very high.
To determine a win %, we need to look at hand strength relative to our opponents range, which is defined by the actions he takes.
Ace high flushes will lose to the following hands:
Straight flushes
Royal Flush
Full Houses
Quads
A Straight Flush will only lose to a higher one or a Royal Flush.
Using Equilab, against a random range, assuming we flop the low straight flush. Our opponent has exactly 1/1326 combos that beat us, which is 6

7

.
In this, we lose 0.52% of the time; we are a 99.48% favourite. Example scenario below:
If we change our 3

to A

, we are 97.33% to win, and our opponent is 2.67% to win. See below:
All in all, if you have the nut flush or the straight flush, you are pretty happy to get your money in and take this to showdown. Also bear in mind the board runout, of course it's not possible to lose against a straight flush unless one came in by the river, so be weary of this in accordance with your opponents aggression, and you should be fine with these hands a very high percentage of the time.
I hope this helps & let us know if you have any more questions!
-E