What do you mean by "ultimate"?
If by "ultimate" you mean blazing and badass, then a Mac II isn't going to be it with 6.0.8.
If by "ultimate" you mean most flexible and backwards compatible, then a Mac II can be that, but you have to plan in those terms.
From a software point of view, the real "strength" of System 6 is the ability to play nice with application software that isn't 32-bit clean. Moreover, since you're talking about a Mac II, you're dealing with a platform that predates System 6.0 by a year and 6.0.8 by four years. Its real strength is backwards compatibility.
IMO, it can be the "ultimate" 6.0.8 system in the same sense that a late G4 PowerMac can be the ultimate Leopard system. Both predate the system software by several years and both have a slower processor than the models that were current when the system software came out, but both can boot in earlier versions of system software and run legacy software that the newer machines can't. And in the Mac II's favor, I doubt it will take the same kind of relative performance hit in System 6 against say, a Iici, as a late G4 in Leopard would against a quad core Mac Pro.
Another thing to keep in mind is that System 6 didn't change that much from 6.0 to 6.0.8. Most of the various releases were compatibility releases modified to include support for newer machines as they were introduced. (Apple tried to avoid these kinds of compatibility releases with System 7 by releasing specific system enablers for new machines instead.) So unless there are features of 6.0.8 you specifically want like better printer or networking compatibility with System 7, you might be better off with an earlier version like 6.0.2 instead. It all depends what you want.
If I were you, I'd probably put System Software 5.1 or 6.0 or 6.0.2 on it try to make it into the ultimate Mac workstation circa 1987-1988 when it was the $10,000 beast, not the aged champ of yesteryear circa 1991 when 6.0.8 and System 7 came out.
If by "ultimate" you mean blazing and badass, then a Mac II isn't going to be it with 6.0.8.
If by "ultimate" you mean most flexible and backwards compatible, then a Mac II can be that, but you have to plan in those terms.
From a software point of view, the real "strength" of System 6 is the ability to play nice with application software that isn't 32-bit clean. Moreover, since you're talking about a Mac II, you're dealing with a platform that predates System 6.0 by a year and 6.0.8 by four years. Its real strength is backwards compatibility.
IMO, it can be the "ultimate" 6.0.8 system in the same sense that a late G4 PowerMac can be the ultimate Leopard system. Both predate the system software by several years and both have a slower processor than the models that were current when the system software came out, but both can boot in earlier versions of system software and run legacy software that the newer machines can't. And in the Mac II's favor, I doubt it will take the same kind of relative performance hit in System 6 against say, a Iici, as a late G4 in Leopard would against a quad core Mac Pro.
Another thing to keep in mind is that System 6 didn't change that much from 6.0 to 6.0.8. Most of the various releases were compatibility releases modified to include support for newer machines as they were introduced. (Apple tried to avoid these kinds of compatibility releases with System 7 by releasing specific system enablers for new machines instead.) So unless there are features of 6.0.8 you specifically want like better printer or networking compatibility with System 7, you might be better off with an earlier version like 6.0.2 instead. It all depends what you want.
If I were you, I'd probably put System Software 5.1 or 6.0 or 6.0.2 on it try to make it into the ultimate Mac workstation circa 1987-1988 when it was the $10,000 beast, not the aged champ of yesteryear circa 1991 when 6.0.8 and System 7 came out.