at range it won't hit as often as a tau fire warrior...
I just wanted to point out that in fact, SMs have better aim than a fire warrior, not only in fluff, but also in the tabletop rules (BS4>BS3) and for sure they are more than likely to splat the little blue man. Better armour save, better hit probability, the same wounding probability, and only slightly less range that can be mitigated with the use of cover? piece of cake! (but they also individually cost more points, for a reason).
The nob in CC is another completely different thing, it would come down to equipment mostly (power weapon? choppa? power claw? power fist?). But that said, nobs are supposed to be really badass in CC, so it's fine by me if some oversized green ape fungus can match my marine in CC, both in fluff or tabletop.
Aaand I also wanted to point out that if you want to go with the tabletop rules to establish SMs individual power, you have to consider that there are several editions of the game, and that in 2nd ed marines (and particularly terminators) were pretty powerful (I didn't play before 2e, so I really can't tell how they were on the beginning).
To answer normtheunsavoury's question, it would depend on the environment. If it was in the open in a straight head to head confrontation, a couple of platoons of guardsmen with a vet unit with plasmas could be enough. If it was in a guerrilla environment, said team could probably take on a whole base (multiple platoons with armoured vehicles, sentinels, etc) by themselves.