Virgin will certainly match any Sky offer but you seem to have several other reasons to want Sky. You almost certainly won`t lose Broadband Speed which you say is currently 2 Mbps but unlike Virgin I think Sky caps the monthly download limit as you say.
A word of warning - I know someone who made the move from Virgin to Sky. She was told that she would have to pay for the following month which is the notice period. Fair enough. Then they cancelled her e-mail account immediately! She didn`t have time to notify all her contacts of the switch and her new e-mail address and the Sky installation took 10 days to materialise on her BT line.