ETpilot
If you are going to be the only person flying from this strip, and you are comfortable with 30 X 150 I say go for it.
But the winds are not all ways kind, our little club about 40 members Has some really good pilot's, and our main runway is 200 X750 with 35" trees 150" from the one end and due to the wind's it some times it is just barley enough, we have 6 to 10 inch grass barriers on all sides.
So if your land is profit growing land then you need to stay as small as possible, if not I would go for a bit larger field, say 100 X 250 this would give you a bit of wiggle room
Just my thoughts
Cheers Bob T