i say not to factor in future ccr/sccr diving unless that's in your plan for the next year. buy a computer one or two steps ahead of where you are, not five steps ahead.
yes, jax, they're all reasonably equivalent. start trolling for a used one & you can score for less than $1k. whatever comes up that you can get is fine.
Not sure I agree that CCR is five steps ahead of OC trimix... imo it's sort of the next logical step (especially after you get your first big gas bill on a trip).