That's a big deep tank and you need a lot of light no matter how you shake it?!
Sticking with Kessil and T5's
That's a Kessil every 2 feet (4 x 90 = 360 watts) and 4 T5's the length of the tank (432 watts), so a little more than a six bulb T5 (648 watts) fixture in terms of par total is my guess. Also, the Aquatic Life (less wide) T5 reflectors do not pack the punch of say ATI reflectors is what i recall, so middle and bottom third of the tank will not be high par, especially if your water clarity (nutrients?) is at issue. If your SPS is in the top third of that deeper tank they'll be fine light wise, nothing crazy, but 200 to 300 par is my guess.
Cost on your current setup is $335.00 x 2 on the T5's, or $670, plus $450 x 4 on the kessils and say another $100 for a dongle ($1900), for a total of $2,570.
Personally, if you stuck with the Kessils you have and added more, for heavy SPS on that 30 inch tank, I'd add three more X500's (185 x 3 = 555 watts), and you would have the light (1,347 watts) to hammer out SPS anywhere in that tank IMO... that would another $2,217.00 ($739.00 x 3). So a very ideal kessil and T5 setup here would be $4,787.00.
Say these LEDs last 5 years, that's $4,115 every five years plus, say $160 a year on T5 bulbs, plus or minus 50% depending on your bulb change schedule.
So $5,587.00 for five years for a very nice kessil and t5 hybrid. If you did away with the T5's and ran just the Kessils (3 500x's and 4 360x's) your cost over five years would be $4,117.00. If you did four 500x's over five years that is $2,956.00 (but i wonder if you would want fill light? In that case, four 500x's and 4 Aquatic Life fixtures over 5 years would be $4,426.00).
Using 740 watts to 1347 watts, depending on the above.
Versus Halides
In comparison to halide days, you would have probably had four 400 watt halides (1600 watts) on the same tank (30 inch!) if you were SPS dominant, so you're (currently in comparison to haludes) not running a lot of light on tank that size and especially that deep.
(Total watts isn't really the best way to measure a LED lights power, but nonetheless the comparison above is pretty accurate in terms of figuring out ball park light needs... The reality is that while LEDs produce less heat (sometimes), they are not that much better/efficient at reducing electrical consumption if you want to hit the same PAR numbers in the tank as halides or T5's....)
Cost of halides, say reefbrite 400 watts would be $534.00 with ballasts and bulbs each, total $2,136.00 for 1600 watts of proven SPS growing power (
https://www.aquariumspecialty.com/reef-brite-halide-hybrid-15-mogul-pendant-kit.html). Each bulb would need to replaced say every 6 to 12 months (at $60 a bulb for reefbrites/$240 every 6 to 12 months/$2,400 per five years, plus or minus 50% depending on bulb replacement).
So over five years, for a nice halide setup that's $3,336.00 to $4,536.00 using 1600 watts.
Versus just T5's
An ATI 8 bulb dimmable 48 inch fixture is $825.00. Need two, so $1650.00. Plus bulbs each year at $400 a year, plus or minus 50% depending on how often you change the bulbs.
Over five years, pure T5's is $3,650.00 using 864 watts.
Versus Reefbrites strips: 16 reef bright xho 48 inch strips is $6,336.00 using about 864 watts
Versus ATI Straton: four of these is $4,400.00 using 920 watts
Versus Neptune Sky
As for Neptune Sky, the ideal setup according them, since they recommend 3 skys for a 72 inch tank, would be 4 skys for the 96 inch tank.
The Skys come in at $869.00 each so--$3,476.00 every five years using 876 watts. If you added an additional sky, 5 total, so every 19 inches instead of every 24, you'd be at $4,345.,00 and using 1,095 watts.
Conclusion:
You're gunna spend some money no matter what on a 8 foot 30 inch deep tank.
But the Sky is arguably the most economical way to go for best coverage on an SPS tank (Four Kessil 500x is cheaper but same coverage?; Halide and changing bulbs once a year is cheaper, but higher electical costs and chiller?...)?! Seems to be a T5 replacement/halide (not factoring in that the T5 fixture/ballast and halide fixture/ballast may last more than five years and still run lights 100% because you're changing bulbs)?! So long as that "one year" warranty holds up and they're not Chinese garbage--seem like a good light
I do question whether the Sky is going to penetrate 30 inches say as well as halides, or the Kessil 500's, however, which can utilize lens designed to do just that....
Personally, i think combo hybrid lights are the best, but lights like Neptune Sky and ATI Straton might change my mind?