My suggestions, (worth exactly what you paid for them, although I'm not experienced with S gigantea, I've nursed one of my H.magnifica's back to health using this methodology...see
This thread "Heteractis magnifica - tell me some success stories" for more on that....)
Start feeding slowly, without clowns in the tank, small amounts every other day.
When you feel like moving the anemone to the display, measure the distance of the anemone from the light, (total distance the anemone is from the light, and the distance the anemone is under the surface of the water) and replicate that in the display tank.
Then slowly, (ie once per month) increase the intensity of the Radion 5%. Once you've reached 80%, you're at about 250 Watt HQI MH 10K bulb levels for par. I base this on my own experience of running 10k XM SE bulbs with my H.magnifica's and then switching over to Phoenix 14K SE bulbs with no change in behavior, (ie no panning for more light no movement to seek higher intensity lighting), and then switching to Radion Gen 1's at 12K setting at 80% intensity level again with no change in behavior, (ie no panning for more light no movement to seek higher intensity lighting).
Obviously this is anecdotal with a sample size of one...but there it is. If your anemone begins to show signs of unhappiness, go back to what you were doing before.
Slow and steady wins this race.
IMO/IME clowns with a weakened anemone, (from shipping stress, tank stress whatever) are a bad idea. I've seen anemones that should have survived killed by clowns that stole food from it. The anemone's attempt to capture and ingest food that is later stolen by clowns is a net loss of energy and metabolic resources that a weak anemone cannot sustain.
If the anemone is not at 100%, IMO/IME you should either keep clowns out of it, or watch them carefully and be prepared to intervene and chase the clowns out of the anemone, (I've used an algae scraper in the past although anything similar will work) until it fully ingests the food item. Once the food item, (small at first) is fully ingested, the clowns can be allowed to return to the anemone.
This can take as long as 60 minutes in a seriously weakened anemone in my experience. You may be "guarding" this anemone for as long as several months, until it is healthy enough to resist the clowns from stealing food from it.
IME, once the clowns cannot steal food from the anemone, you've won, and the anemone should survive barring any further complications.
Good luck, and once again, I'm jealous.
You have a beautiful anemone that looks like its on the right track to becoming a show piece of your tank.