v1.3.8 "with patches" is not something to hang your hat on. You're still vulnerable: There are some complicated security fixes for 1.3.8 which were NOT released as a separate standalone patch, because they were as much work as an upgrade. SO, they were rolled into v1.3.9.
This is what I recommend:
If you wish to "get the jump" on going to 1.5.0, do your upgrade to 1.3.9 for your site NOW, and then AFTER you've taken that upgrade live, start with preparations to take it to 1.5.0 whenever it's released ... collecting and testing addons etc using the beta and then doing the actual real upgrade using the official version when it's released.
Make sense?
Your second upgrade is always MUCH faster and easier than the first.
The code changes from 1.3.8 to 1.3.9 are easier to identify and customize than they are when jumping from 1.3.8 to 1.5.0. Smaller steps are much easier to take.
Plus, if you have addons that need upgrading for 1.5.0, then at least you buy yourself some time by having your site at 1.3.9 already.
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