The 04-07 FX HOs are pretty similar. Yamaha just made some minor improvements to internal parts over that time period. The 08 model had the most upgrades including a new hull material and design. The 09 and later have a completely different engine (1800cc), and are basically a completely different machine even though Yamaha still uses the same designation.
The 04 did have a recall for how the wiring harness was mounted that was corrected on later models, and would have probably already been corrected on the one you are looking at. There was also a problem with the motor mounts cracking and breaking on the earlier models, so I'd try to get a look at them or see if they have been replaced (not a big expense if you do it yourself, but labor intensive). Much more common if the ski was used for wave/wake jumping.
Hours are much less important than how the ski was cared for and whether it was used in salt water or not. I've seen 04 skis with less than 50 hours with totaled engines, because they were left for long periods without proper care, and other ones with over 500 hours running great. IMO salt water use causes significant deteriation, unless very thorough post ride care is taken.
Most 04s regardless of the hours are going to be prone to parts failure just like any other 6+ year old ski.
That ski should do around 58-60 mph at around 10,000 rpm. If it runs good in the water, you should be OK.