I see the Major 7th to Octave leading tone progression you describe (for example C,B to C, C) as implicit in a V to I cadence of G7 to C. It's what is known as a suspended cadence where the V has a 3rd (B) and a 4th (C) which anticipates the tonic C. The absence of a b7th (F) just means that there is no voice leading to the Major third of the C tonic (E) should you wish to include it in the cadence.

Similarly if I played the b7th (C,Bb) I feel it does have a strongly implied resolution, this time a semi-tone downwards to the Major 6th C,A. Again it's an implied V to I cadence partially stated. This time the cadence is C7 to F major with A functioning as the third of F which is the tone omitted on this occasion but as in the above example, strongly implied nonetheless.

As for an order of dissonance on the tonic I would say the next tone you might try is the b5th preceded by a bII dominant. After that you could try the Maj7#5. Next up in the dissonance food chain would be a b3 against the 3rd giving you the Maj7#9 chord. I would be careful with a b9th; it's best voiced as 1, maj3rd, maj7, b9, 5 but still not to your liking even when using a bII alt7 as the dominant to lead in.
The 4th doesn't sound resolved enough in a third based context, the b7th on the tonic sounds okay in a blues progression but not on a standard maybe!

Bear in mind that truly dissonant sounding chords wouldn't so much substitute one tone for another but play both together (i,e b7 against maj7, b3 against maj 3rd)and with more than one semi-tone clash present simultaneously). Including colour tones, extensions or changing the chord quality is not necessarily by itself dissonant sounding. There has to be a feeling of 'disagreement' or contradiction in the voicing to some degree where the implied function and tonality is obscured.

Alan