Oh yeah,
"Track per track", there's less headroom on the 488, as compared to the 424. The audible difference will be there, track per track, however subtle it may be.
The upside is, that the 488 does have twice as many tracks as the 424, and depending on your recording techniques and program material, "overall" [cumulative] headroom should be relatively equivalent, between the 424 and 488.
It all depends how much you value the integrity or strength of each track, versus the value of the number of tracks. There's definitely a tradeoff on that.
If you want individually stronger sounding tracks, stick with the 424.
If you want twice as many tracks, and don't mind sacrificing a little of the relative strength of each individual track, going for more production value thru more tracks, then go for the 488.
I think people with 488's or 238's generally like them, and I've seen comments about how good the sound is, despite the narrow track width.
Again, I think, "overall" sound quality should be relatively equivalent, between the 424 and th 488, with the 424 having slightly stronger sounding individual tracks, and the 488 just having more, slightly weaker sounding tracks.
Take one of each, they're small.
Make sure you stick with the mkII model, minimum.