kaner, I haven't heard that the programs are merging. I had stated earlier that the programs remain independent. Where did you hear that the programs are merging? Yes, you could convert Diners points to Westin if you wanted (though I think that the Diners promotion for double British Airways is a much better deal).
Catman, you get a complimentary 1 year SCI gold membership with the Sheraton Optima, so that could save you $25 for the first year. Also Sheraton Optima gives you 1 mile for every dollar so $25000 charged can get you an airline ticket. You need to charge much more with the Hilton Optima to get a free ticket. AMEX now lets you have both cards.