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These things are a bitch to design but once it's working as intended and the niggley problems addressed it should beat any hard switched approach hands down.
This is precisely why I did not recommend any kind of resonant or quasi-resonant topology to the OP. This will be his first smps design, after all...
In fact, anything more complicated than a low voltage buck converter is likely to be more of a learning experience than the OP expects, but rather than flat out discourage him (or insult him into hiring a pro to design it for him - a curious marketing strategy, that), I instead chose a topology which is rather forgiving to design and highly tolerant of abuse.
For example, any kind of modulated bridge converter is almost a non-starter because the layout and timing of the bridge switches is very critical which means extra attention needs to be paid to the gate driver design and layout, and this is experience that one tends to acquire from, well, experience. Ie - not only blowing stuff up, but learning from the bits of shrapnel and escaped magic smoke. Thus no type of modulated bridge is suitable for a beginner.
Resonant (frequency modulated) converters are downright nightmarish to get working correctly, and operating on the wrong side of the resonant hump, or with the wrong Q, or about a dozen other arcane to mundane restrictions, can get you into trouble fast. It's hard enough for people like me who've been designing smps for 20+ years; I certainly wouldn't recommend it to a beginner. Frankly, I only recommend resonant converters for specific and highly reactive loads like, for example, transverse RF-excited CO2 lasers or high power ultrasonic transducers.
Quasi-resonant (aka resonant transition, lossless transition, etc.) can combine the wide load range performance of hard-switched with the (sometimes, not always) lower losses of resonant, but also seem to combine the worst traits of both converter families when it comes to designing them (especially those which require an auxiliary switch network to achieve lossless switching).
Even if you possess the requisite knowledge and experience to design any kind of converter, real world constraints often steer you away from the more exotic even if theoretically ideal topologies. Unless you design LLC converters every day I can guarantee you it will take much longer to get one working than a buck fed bridge, and at some point just the sheer difference in design time outweighs any potential operational efficiencies, especially for an intermittent load as I imagine an x-ray tube to be.