UPDATE:
Well, not a lot of feedback on my post :-). Based on research - and almost nothing from Pearson! - typical guidelines are to tension to 10%-15% breaking strength of the wire (racing boats up to 20%). Without going into a lot of detail, I took care the mast was straight, and introduced a small rake (yes, our big thick masts do bend!), and tightened the rig...
(as an aside: Our lower shrouds are 1x19 316 s/s. 1/4" BS for 316 is 7,600lb; cap shrouds and stays are 9/32", with a BS of 7,800lb)
New tensions:
Aft lower: ~580lbs
Cap shrouds/upper: 750lb
Fwd lower: 800lb
Backstay: 980lb
With the rig tuned like this, I was able to point ~5% higher. And my leeward shrouds no longer flop around in moderate (15-20kn) winds!
Ideally I would have put a little more on the fore/back stays - there is still some headstay sag - but noticed that as I added a couple more turns on the turnbuckle, the tension did not increase. However, after measuring the fwd-aft length of the boat, the hull was beginning to bend. So I guess the was not designed for a really tight rig, and I think around 900lb may be optimal.
Well, that's all for a bit. I just pulled the chainplates (which were actually in good shape! Oh, well) so more experimentation will have to wait for a while. But this has convinced me that (within moderate limits) tuning the 323 rig can improve performance. Yes, possibly "duh", but...