Heavy British intervention might come at the cost of abolition, gradual or otherwise. I believe the UK was ready to support CSA independence in 1862 in exchange for abolition but it fell through when the South said no. In many ways the leadership and inept diplomacy of its own diplomats were a key part of the downfall of the Confederacy.
An "ideal" victory scenario to me would depend on people who faded into shadow after 1862. Sibley needs to win in Arizona/New Mexico and create the illusion that the Confederates might have a chance to invade California. Perhaps he can work with Mormons in the area and the promise of an independent state for them if they aid the Confederacy in cutting off the West and its resources from the East as much as possible. Nashville needs to stay Confederate if at all possibleor barring that Bragg needs to be able to hold onto Kentucky, which in my opinion was looking to see who would win the war before most of her citizens would commit themselves heavily either way. Missouri would probably be a negotiating ground as would West(ern) Virginia, though the areas south of the Missouri River were held by the rebellion in the early part of the war. Western Virginia becomes more problematic as the northernmost counties wanted to secede, I could see Wheeling leaving and joining Pennsylvania for the sake of their people and simplicity of border control. Get some of the nothern Mexican states to join in as well, Nuevo Leon and Coahuila if not Tamapulias, Sonora, and Chihuahua could make Confederate states with seemingly little hope of Mexican recovery after Maximillian comes along. All in all I think you could get the original Confederate states with Kentucky and Western Virginia restored, Missouri is unlikely and would be split at the Missouri River at best. Arizona and the Indian Territories are not unreasonable and perhaps New Mexico if the West turns out very differently. Add anywhere between two and five Mexican states (not sure how Baja California plays out) and that's the best you get in any TL in my opinion. BTW I do not think the Confederacy could survive with anything less than the original 11 states that seceded, if they try they're likely bankrupt in 15-20 years or end up like a desperate banana republic with heavy dependence on a few cash crops and notable class division.
An "ideal" victory scenario to me would depend on people who faded into shadow after 1862. Sibley needs to win in Arizona/New Mexico and create the illusion that the Confederates might have a chance to invade California. Perhaps he can work with Mormons in the area and the promise of an independent state for them if they aid the Confederacy in cutting off the West and its resources from the East as much as possible. Nashville needs to stay Confederate if at all possibleor barring that Bragg needs to be able to hold onto Kentucky, which in my opinion was looking to see who would win the war before most of her citizens would commit themselves heavily either way. Missouri would probably be a negotiating ground as would West(ern) Virginia, though the areas south of the Missouri River were held by the rebellion in the early part of the war. Western Virginia becomes more problematic as the northernmost counties wanted to secede, I could see Wheeling leaving and joining Pennsylvania for the sake of their people and simplicity of border control. Get some of the nothern Mexican states to join in as well, Nuevo Leon and Coahuila if not Tamapulias, Sonora, and Chihuahua could make Confederate states with seemingly little hope of Mexican recovery after Maximillian comes along. All in all I think you could get the original Confederate states with Kentucky and Western Virginia restored, Missouri is unlikely and would be split at the Missouri River at best. Arizona and the Indian Territories are not unreasonable and perhaps New Mexico if the West turns out very differently. Add anywhere between two and five Mexican states (not sure how Baja California plays out) and that's the best you get in any TL in my opinion. BTW I do not think the Confederacy could survive with anything less than the original 11 states that seceded, if they try they're likely bankrupt in 15-20 years or end up like a desperate banana republic with heavy dependence on a few cash crops and notable class division.