Man... I'd have a hard time telling any of those Matrox cards apart. I'd expect the G400, G450, and G500 to all be excellent and maybe indistinguishable unless you have an excellent CRT and excellent eyesight. If anything, VGA analog output quality might have gotten worse after that point (less incentive to put money into analog output if most customers are using DVI-D).

Out of the cards I have I cannot tell the difference between my Voodoo 3 3000 AGP, Radeon 64MB VIVO, Radeon 9800 Pro, and Radeon X850 Pro. They all output clear image to my 19" CRTs at 1600x1200@60Hz and 1280x1024 @ 85Hz. The nVidia cards I have of similar era tend to look worse...

Maybe sometimes might also be a matter of card PCB components lifetime who knows, but I sure remember seen improvements comparing the G400 with the G450 and not even at highest resolutions, the pixels were sharper and cleaner, the noise (especially not to mention when are used passthrough cables like add-in cards required) reduced, the colors etc..of course the G400 is equally great, it might be difficult to see any difference but I'm convinced there were improvements; after the G450 I had difficult time to compare it to the G550, I don't have an high end time correct monitor and that would make some difference but still I think they got the best from what the VGA output could at least as an obsolete connection (obsolete more or less.. 2013 cheap monitors even 1080p still had that connector).

Late low-profile G450s use identical components and PCB with G550.