If you're happy with the current saddle, leave it.
You can do a groupset change in bits and pieces, but the new 105 is 11 speed, so you need to know if your current wheels can take an 11 speed cassette. If you're changing the wheels, most are now 11 speed compatible anyway.
It can be cheaper buying the groupset complete too.
You can do a groupset change in bits and pieces, but the new 105 is 11 speed, so you need to know if your current wheels can take an 11 speed cassette. If you're changing the wheels, most are now 11 speed compatible anyway.
It can be cheaper buying the groupset complete too.