The only boat that I know of that works that far down is Tony Wass's Old Offshore 32 "Claire Gail" I think its called. Tony works from Girvan, I've dived with him a few times down that way on the "Esbo" 35m, which was quite good and round Alsia which was pretty shite.
We were supposed to dive with him in May but got blown out so did the Wallachia and Akka with our club boat instead
The weather is much more critical when you get South of the Cumbraes as the sea opens up and is more exposed to winds from all directions, where as North of the Cumbraes you can usually get enough shelter to do some of the wrecks.
Andy G