I believe the 2 shares will move in unison and there will never be a great difference. GBG will be around twice the price of GBG.
I believe the deal will go through, security of GBG combined with the speculative nature of SDL, a nice balance for me.
I held both until yesterday, I sold GBG and bought twice as many SDL and made a nice margin by doing so, assuming the deal goes through..........
