Feat 1: Ephialtes deflects lightning.
"Jason called down another lightning strike, but Ephialtes caught it on his spear and deflected the blast, melting a life-sized plastic cow."
Mark of Athena, Page 528 in Hardback, ISBN: 978-0-141-33574-2
The giant is stated to be 12 foot tall. The spear is stated to be 10 foot. For the sake of the calculation, I will treat the tip of the spear as moving in a curve from parallel to his body, considering that he would have had to have gone from there considering that he was moving to attack.
10 foot=3.048 meters.
12 foot=3.656 meters
That can be considered the radius.
Circumferance=pi*2r
=pi*2*3.048
=19.2 m
Distance moved is 1/4 of circumferance.
Distance moved by spear tip=4.79 m
So, for him to deflect the lightning, he would have to hit it before it could reach him.
2100-3.56=2096.344
Speed=Distance moved by spear*Speed of lightning/Distance moved by lightning
=4.79*4.4*10e5/2096.344
=1005.3 m/s
Or Mach 3.
Feat 2: Jason blocks lightning
"The second spirit let loose a bolt of lightning, but Jason's blade absorbed the charge."
Firstly, to support using the lightning speed here is that, like other spirits, the Venti are embodiments of forces of nature. In this case, storms. As such, it is safe to assume that they act as sources of natural lightning.
Now, for distance I will assume the lightning travelled the length of the skywalk they were fighting on.
According to wikipedia, https://en.wikipedia.org/wiki/Grand_Canyon_Skywalk , the length of the skywalk is 70 feet, or 21 meters.
Based on other events in the series, Jason and Thalia need to move their weapons into the path of the lightning in order to absorb it into their attacks.
Iulius was in gladius form, so I will go for the length of a historical gladius unless someone can find a stated length for the weapon.
Low end gladius length=0.65m
High end gladius length=0.85m
Source: https://en.wikipedia.org/wiki/Gladius
For the sake of the calculation, I will use 1/4 of radius again as a fair estimate.
Distance moved by sword (Low end)=1/4*2*pi*0.65=1.02m
Distance moved by sword (High end)=1.33m
Speed=1.02*4.4e5/21
=21371m/s
Or Mach 62 for low end.
Speed=1.33*4.4e5/21
=27867
Or Mach 81 for high end.
So High Hypersonic for this feat
Feat 3: Percy's destroys a glacier
"Then he slammed Riptide into the ice at his feat. The entire glacier shuddered. Behind Percy a wave surged up from the bay- a wall of grey water even taller than the glacier. Water shot from the chasms and crevices in the ice. As the wave hit, the back half of the camp crumbled."
And the amount of destruction caused is made evident on page 470:
"He stood at the edge of the glacier, leaning on the staff with the golden eagle, gazing down at the wreckage he'd caused: several hundred acres of newly open water dotted with icebergs and flotsam from the ruined camp."
The glacier in question is Hubbard Glacier.
Now, to calculate the energy to destroy the glacier.
I will treat the volume as that of a prism, with the area stated to be destroyed as the area of the main face.
The word "Several" means more than 2 but not many, so I will lowball to 200 acres.
Area: 200 acres= 809371m2
According to this, http://www.barrier-freecruising.com/features/alaska-hubbard%20glacier.html , Hubbard Glacier is 600 feet tall.
Height: 600 feet=182.88m
Volume=809371*182.88=148017768.5m3
Fragmentation of Ice= 0.5271 j/cc
148017768.5m3=1.408177685*10e14cc
1.408177685*10e14*0.5271=7.80*10e13j
18.647 kilotons of tnt. Town level.