What are your goals in upgrading?
105 components are already quite good, and the bike is mostly 105. While 105 cranks will probably likely shift a bit better, perfect front shifting rarely has much impact on performance. Front shifting is more of an annoyance than anything. and you would be hard pressed to notice any stiffness or weight differences from the cranks that are already spec'd on the bike.
If speed is the priority, removing drag from your clothing and position will be the first place to start. Skin suits (or form fitting kit) and low drag helmet will be the biggest bang per buck. Next up, wheels can also be a good upgrade, but to be honest you will likely need to spend more than the cost of the bike before you will really notice this upgrade.
If you are upgrading simply to out do your friend or riding partners, well then all that matters is what matters to them. Ask questions and I am sure they will tell you to through your money.
Just an opinion
Honestly, the best would be to focus on maintaining the bike, ensuring your clothing and contact points are comfortable and just ride your bike. As it stands you have a good entry level bike. The performance should be quite good, getting that extra bit of performance that remains will be very costly endeavor if you take the upgrade route. When you are ready for a faster bike, save and purchase it outright. Used or old new stock can be a very economical way to go. I would largely avoid the upgrade game as it is often 10% performance, 90% playing with money.