No need to get overwhelmed. I would go with a 23mm up front, either a Grand Prix TT or Corsa Speed. You could go 23mm in the back or a 25mm either is a good choice.

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Thanks Thomas. What is the reasoning for potentially doing a 25 in the back vs the 23?

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It was more because you suggested it and I didn't want to rock the boat. Riding a 23mm is fine too in the back. I wouldn't sweat it either way.

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I'd go with the 23mm Attack up front and a 25mm TT in the rear.

I think the 23 TT is supposed to have a lower Crr and very similar profile to the Attack 23, but my guess is they are the same tire with the Attack having some little tread things molded onto the sidewalls.

I would consider tire frame interference before trying a 25. I tried the 23/25 Attack/Force on my Venge and Speed Concept. Neither frame is new enough for the 25 Force to have been considered during the design process. This makes getting the 25 into the frame very tight fit. Easier to put the tire in the frame un-inflated and the Speed Fin on the SC has to be exactly centered. I took the Force off and am running a 23 TT now and it works just fine and seems to wear well.

Unless you know a 25 fits well in your frame, I would just go 23 GP TT front and rear and not overthink things. The 25 has some aero penalty and some WAG estimates of additional drag from Josh Portner make the Crr/Cda saving/difference a wash. If you have tons of room the 25 MIGHT be a bit more comfortable ( I didn't notice a difference) and it may be a bit better on really rough roads.

Personally I don't think the Speed Fin is worth enough time to warrant the difficulty of removing any wheel/tire combo from the SC. I replaced mine with the UCI brake cover and things have been much easier since. The 24mm Attack was an absolute monster and barely fit in my SC. I suspect the 25mm Force is just the old 24mm Force re-labeled to be a little bit closer to reality.

WRT the GP TT and the Attack, it's the same compound, same breaker, and the TT has a touch thinner tread (so slightly better crr). For fast riders the Attack is probably the better choice. It's pretty damn aero as tires go and it has tested well on lots of wheels (Hed, Swisside, and one other I can't recall atm). The Attack seems to have a Scarlett letter on it for no reason because of some (faulty in my opinion) crr data out there. For example, BRR.com compares the "22mm" Attack to the 25mm GP TT and the 25mm GP4000SII without adjusting the pressure. IMO that's a legitimate critique of TomA's roller data as well and, IIRC, he's mentioned adjusting these results in the future to account for estimated casing tension.