I believe the top speed of the ringship we saw in "Breaking Ice" was established as warp 6.5, whereas the similar-looking but a bit larger and differently engined ship from "Fallen Hero" was capable of warp 7. Those would be dash speeds, not sustainable ones, most probably... The significantly larger warship type introduced later in the show (the one with the pivotable ring) could be assumed to be capable of similar speeds.
The ship from "Fusion" was reused as a military vessel in the Season 4 Vulcan trilogy: two of them accompanied one of the big tilting-ring warships in pestering NX-01 on Vulcan orbit. While one of the VFX shots suggests that the "Fusion" ship was really tiny compared with the hero vessel, most of the shots do not give us a chance to compare sizes, and the dialogue establishes the "Fusion" ship as a "cruiser". What should we make of this? The vessel type was supposed to have been retired two centuries prior. Did the Vulcans de-mothball some old vessels in a time of approaching crisis? Or did this ship type remain in service within the Vulcan system, merely retiring from interstellar duty?
Vulcans may have had decent warp thousands of years before ENT, losing much of their tech in the war that killed Surak, and then slowly regaining it. What this means for the top speed of a 200-year-old or older ship type is unclear. Perhaps Vulcans regained the old tech all at once, after recovering industrially - meaning that all ships in the past 500 or 1,000 years have been capable of warp sevenish. Or perhaps there has been a relearning curve, which would make the "Fusion" ship slower by some unknown amount. We're free to speculate...
Timo Saloniemi