Serious in an informal context confers indeed the meaning of "very well up to the job, actually oversized for it!"
Big-ass can be used in the same (very informal) way.
High-end on the other side, means that it is on the high-end of a technological, quality and / price scale. It may be very advanced, very good en very expensive, but not usable in a corporate environment.
So when you say you have high-end equipment, it doesn't mean it is big or enterprise style.
When you say you have a serious (or big-ass computer system), you may be talking about an actual mainframe in your basement. Now that is a serious computer!
On the other end, if it is an original 1960's model, I would hardly call it high-end!
The newest iPad mini is certainly a high-end gadget, but it is hardly a machine aimed at the corporate market.
If I buy a modern 4 port optical switch for use at home, that probably is a high end switch (are there budget versions for glass networks?)
However, where I work, they prefer to have rack-mounted 32-port manageable gigabit network switches with redundant power supplies and fail-over options. Those are not as high-end as my own switch, by far. But they are bigger, badder and more serious then my fancy toy :)