I have used 5/8 Fire ring on my skates for most of the last 18 months or so. I am 6'4" and while I'm now 245 or so, I did weigh close to 285-290 in the early summer which made me even slower than I should have been for 45. I'm back to skating a lot better and have stuck with the 5/8 Fire as it gives solid bite with ridiculous glide even on fairly soft ice. On occasion, on some of the ice here in Texas in the summer, the 5/8 Fire is like a 1/2 ROH, but it is still my choice. The notable exception is our newest StarCenter which has, bar none, the best ice anyone in my family has ever skated on, to include rinks in Chicago, Toronto, Minnesota, Colorado, Arizona, New York, Missouri, and Iowa...it's that good. On that rink, the 5/8 Fire feels a tiny bit too "loose", bit I find that if I get really low in my stance and actually bend my knees properly on each stride, that significantly changes the bite I get. Almost all of the time (i.e. unless I'm skating at the new rink and it's also very cold and dry), I prefer the 5/8" to the 1/2". I have done the 3/4 Fire a couple of times in the summer when the humidity was high and the temps were also over 105. Mostly though, the 3/4 Fire gets used as the "cross grinder" since Sparx won't sell me an X-Ring for the home sharpener.
My wife is about 5'8" and 130 pounds, and hates not having massive bit, so she demands the 3/8 Fire when hers need sharpening...not that she'd know when that was because I usually just sharpen them every week before we play (best way to not get chewed out for playing hockey on the weekend is to have your wife as your D partner). My 13 1/2 year old is about 5'6" and 150, and wavers back and forth between the 1/2 Fire and 5/8 Fire. On the home rink with the concrete hard ice, he wants the 1/2 Fire (he says it is just like a 100/50 FBV), but at some of the older StarCenters with softer ice, he'll have me do his 2nd set of steel at 5/8 Fire so he can switch after warmups if needed.
I've not had as many good skates when I try the various ROH rings as I have the Fire Rings, but I suppose that's because since I started getting the 90/75 FBV, I've been able to tell whether someone gave me a FBV cut or a a similar ROH because at my size, the bite is about the same but the glide from ROH is inferior.
As for my Sparx as a whole, I love it. We have VERY few decent sharpeners here, and even the supposedly good ones tend to murder skates on occasion.
I haven't used my Sparx as much for others as I would have liked since my older son graduated and his teammates are using the Sparx at the rink to sharpen their skates when they work there, and most of my younger son's team is simply not good enough to be able to tell the difference between new steel and well sharpened steel and wouldn't be interested in compensating me fairly for my efforts. Other than learning to get better at doing custom Kydex shot blockers for my family and a couple of friends, I'm not doing any stuff for anyone other than my 13 year old, my wife, and myself. I'll tell you that while in actual cash spent on sharpenings, I'll probably never break even. However, as soon as you throw in gas, tolls, and my valuable time (estimated at my 1/2 my hourly rate at work is still $40+ round trip per sharpening visit), I'd bet I've already broken even. Accounting for the fact that I never send anyone in the family out without exactly even steel (the Sparx edge checker is really handy for sure), I'm ahead as far as I'm concerned.
My next project, since my Sparks is significantly out of warranty, is to figure out how to find a good (but relatively quiet) wall-mounted shop vac and build a vacuum filtration system that mimics some of the features of the Sparx commercial unit, but better because it isn't underpowered. I need one in the garage anyway, so a dual use for it would really make it worth my while.
I know this was more than what six501 was asking for, but since I've had about 18 months of lots of use on my Sparx, I figured I'd throw the rest of this in too.