Used SRAM RED Double Tap vs New Ultegra 6800

Hello there!
For a long time the the search function has don't the job for me but now its time for my first time asking for specific advice.
I am buying a used Ritchey Logic Road frame and the seller offered me a "not much used" but "old" Sram Red 10 speed double tap for only €300/$340 with it. My plan was to get a new Ultegra groupset that is currently being sold online for only €550/$620 but now I am not quite sure what to do.
Whats the "better" group set? Is the 10 speed a disadvantage? Double Tap vs. Shimano STI?
All I can say for now is that I am very happy with my current Ultegra 6600 and that I prefer the grey Ultegra 6800 a little over the silver RED. But just the looks won't make me spend almost double the money.
I am very mich looking forward to getting some opinion on this
Best, b
For a long time the the search function has don't the job for me but now its time for my first time asking for specific advice.
I am buying a used Ritchey Logic Road frame and the seller offered me a "not much used" but "old" Sram Red 10 speed double tap for only €300/$340 with it. My plan was to get a new Ultegra groupset that is currently being sold online for only €550/$620 but now I am not quite sure what to do.
Whats the "better" group set? Is the 10 speed a disadvantage? Double Tap vs. Shimano STI?
All I can say for now is that I am very happy with my current Ultegra 6600 and that I prefer the grey Ultegra 6800 a little over the silver RED. But just the looks won't make me spend almost double the money.
I am very mich looking forward to getting some opinion on this

Best, b
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Posts
But that is just my opinion, formed because I started on Sram Red when I got my first road bike
SRAM are a bit like marmite for some people; you either love it or you don't. Personally I wouldn't use anything other than SRAM as the shifting is just logical for me and the hood size is a perfect fit for my hands.
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Yes didn't read it clearly and assumed it was like for like 10 speeds being compared.