John,
There are two restrictions that you have to look at, so you really have to decide.
The real issue is that you need a line of some breaking strength, and assuming sta-set x at 3/8 works, well work with those numbers. Assuming you need 120' of line (40' assumed mast height x 3) that means that the sta is going to run around $140 for the line. Not bad really, but let's take a look at high tech lines and see what they cost would be.
To go to 3/8 amsteel blue, which is my current favorite for 120' at 3/8 you would spend around $330. But the line is roughly four times as strong 19,600lbs vs 5,500lbs breaking strength. And the amsteel will stretch a fraction of the sta-set at working loads.
If instead of sizing for diameter you size for breaking strength you actually save money. Since the same strength amsteel would only run about $110. But it would only be 3/16 which may be to small for your jammers, and can be hard to handle.
The last option is to go to endura braid or similar, which is a amsteel core, with a sacrificial cover. When sized for strength you either have to go down to 4,000lbs 1/4" or go up to 7,000lbs 5/16" which would cost $156 and $230 respectively.
Finally you could go to endura braid, but taper the line, which leaves the core uncovered for the working portion (inside the mast). This is fine for halyards since the tail of the line won't carry much load when hoisting sails, and it is really only when up that it takes much load, but not so good when the line will be used for lifting dingies since the first 20' or so of lift relies just on the empty cover. It does however allow you to buy less line and can save money for something that is just a halyard. Basically by stripping the halyard you only need to buy 2/3 the amount of line you otherwise would, while keeping the same working characteristics. Since the loaded portion of the line is just from the top of the mast down to the spin locks.
Personally all my my halyards are tapered endura braid, except the spare jib which is solid amsteel blue. This allows me to have one 'working line' for sending people to the top of the rig, and hauling, while at the same time keeping costs reasonable for the boat. but I also designed this from the ground up, and have a racing boat, so cost is a little less of an issue than for most cruisers.
In addition to cost however the amsteel is a much more flexible line, and stretched much less under loads. So sail trim and halyard tension is easier to get right, and you get less stretch as the wind picks up. The relative value of this is your call though.
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