[PoetryInMotion]

Dear wonderful helpers at CF. I have a question about nucleophilicity. I want to compare these two reactions with respect to rate:
 
CH₃-I + ^-OH  CH₃-OH + I^--

and

CH₃-I + Cl^-  CH₃-Cl + I^-.

The solvent could be either a protic or aprotic one, I am interested in both cases. Sadly enough, I must say I am completely lost here. There are so many aspects of this problem which makes me really confused. So I hope you can help me sort this out.

This is what I know about the advantages of the respective nucleophiles:

Hydroxide ion
Less polarizable (i.e. worse stablilization of its negative charge)
Better size of the HOMO for σ*(C-I) interactions.

Chloride ion
Higher and thus more accessible HOMO

I also know that chloride ions are softer than hydroxide ions, and that CH3-I is a rather soft acid. Does that matter?

As for the solvent, I suppose that the chloride ions should be favored by protic solvents and disfavoured by aprotic ones (compared to hydroxide ions).