I've got some PAR comparisons between the two in my build thread as my old tank was running Sols (all with 70 degree optics as opposed to the 70/40 combination from the factory) and the Vega fixtures on my new tank. Although I had higher PAR readings with the Sols, my Vega fixtures put out enough light that I recently had to back them down from about 75% to 60% due to bleaching.
The lenses in the Sols are 70 degree and 40 degree, which can be swapped out for whatever combination you prefer, while the Vega uses 80 degree optics. The Sols are better at penetrating deeper because of the tighter optics options.
The Vega must be used with the new wireless controller, which also does give you coral acclimation and sweeping cloud cover modes in addition to your regular moon phase and lighting storm effects modes. The Sols can also use the new controller via hardwired connection unless you get the wireless upgrade for each Sol.
The Vega does use fewer LEDs than the Sols but as mentioned, draws more power due to the larger 5w main LEDs. The Vega Color with the red and green LED's gives you more output in those spectrums.
AI Vega - Technical Specifications
All Vega fixtures use the PowerPuck that will allow you to order custom pucks in the future with whatever LED combination you want (i.e. if you want to add violet or UV for example) and the Vega also has 20 channels of control instead of 3 channels for the Sol. That gives you the potential for a lot more control on the Vega if you go with different LED colors.
The Vega heatsink is also designed to work with the AI EXT mounting system and gives you a little more flexibility with how the light slides on the rails. The Sols can also be used with the EXT but mount differently.
If you get a Sol and want to upgrade to the Vega later AI has said the upgrade will be $250.