The -98i will never run out of hot water, but it'll be slower in filling the tubs, and the installation costs will likely run considerably higher. You may even need a new gas meter/regulator to handle the burner size, which is ~5x the size of your current HW heater, whereas the Vertex burner is less than 2x bigger for input, more than 2x bigger for output.
The Vertex is probably the simplest replacement, and I'm guessing it'll meet your needs, being 2x faster on recovery than what you've been suffering through.
As a point of comparison, I have a 48 gallon indirect that I keep at 130F, and a modulating boiler that delivers about ~50K of output to the tank once the tank has dropped under 110F, and falling to about 25-30K when it's finishing a burn when the tank is near 130F. With this setup 5-10 minutes after full depletion on tub fill it's possible to take an "endless shower", endless only due to the ~25 KBTU/hr being returned by a drainwater heat exchanger. My hot water performance on showering after tub-fills is about the same as what you'd get out of the Vertex, but in my case, only due to the drainwater heat exchanger covering the difference in burner output. With the Vertex, once it has recovered to about 105F (a typical shower-head output temp), the burner alone is sufficient to keep up with a 2 gpm shower literally forever- you don't need to wait until the burner kicks off with the tank at the full setpoint temp. It won't keep up with a 3 gpm gusher shower forever though (but with drainwater heat recovery it could), nor will it support a six side-spray luxury shower for very long.