Ive got two GT Grades, one is the tiagra its stock except mudgards and a 105 chainset which i now use as my winter bike. The other is the Sora one as above but with everything upgraded full ultegra disc, crosslight wheels, carbon seat post, ti saddle and light weight bars not carbon as i use clip on tri bars. it which weighs a smidge over 9kg with pedals.
I’ve used the tiagra version in the pyranees including a ride with 4000m of climbing and on 200km audaxes and it was great, super comfy for me. The only problem was the stock pads wore quickly on the decents and the stock wheels/tyres are heavy but bombproof.
I use the posh one as my summer bike as i need something for the cols that can also do forest tracks but i’ve also used it on a hilly half ironman bike leg and it was fine for that too.
Having used the two for the past year or so, i dont think there’s that much in it except i feel i’m riding a nicer bike and the brakes are better on the posh bike. I weigh that much the difference in the bike weights makes no difference in real life.
Watch out for sizing the Large Grade is massive so definately throw a leg over one before you buy.