But, how often and how much for bulb changes, 8 4 foot t5s at 24 bucks a pop, 192, plus 3 400 watt metal halides at 83 bucks a pop and your looking at about 440/year in bulbs if you change them once a year. Still cheaper than running Radions for a bunch of years but, every year, things get closer. Also, if you replaced the 3 metal halides with three Radions, you'd cut the electric for those fixtures by about half. Again, it may be a long time before Radions become the cheaper option but, as the meter spins, the cost difference decreases. Assuming conservatively 12 XR15s at 420 a pop, you'd be at 5 k for lighting, so just about a 10 year 'break even' before accounting for electrical costs (1200 watts for all Radions run at 100%, which is unlikely, versus 1200 watts of metal halide plus 432 watts of t-5 (actually more I assume because of ballast consumption).
There is certainly nothing wrong with a MH/t5 setup, many consider it the 'gold standard' of SPS lighting but, I like my sunrise/sunset and changing color temp over the day (and, my SPS don't seem to mind) with my 3 Radion XR30 G2 pros and 4 5 foot t-5s over my 180 (still some bulb changes I know). My guess, and its only a guess at this point, is I could light my tank with 6 G5 XR15s without t5 supplementation because of the much improved lighting spread on the new fixtures. With an 8 foot tank like yours, I'd start with 8 XR 15s and see how that worked, planning to add 2 to 4 more if I wasn't happy with the lighting spread initially or had shadowing issues as things grew out.
Too each is own. If you don't like Radions, don't buy them. You can certainly have success without them but, you can also have success with them. If you're not an equipment junkie and part of the fun of the hobby for you is achieving great results on a low budget, that's great (it also shows people you don't need a ton of cash to be successful). But, if part of the fun for you is trying 'the latest and greatest', that's cool too (it helps the hobby evolve). I'm happy to have options. Just don't get me started on people who pay 1k+ for a skimmer that works the same as skimmers that are half the cost.......... Happy reefing.
Matt