Sattelite connection gives around 900 - 1000 ms ping. Server issues can also cause ping to reach that in prime playing times for other broadband type users.

Ok, I'm home now. Time for my own sanity check of the math:

Marginally, 1 Spi = 1/8 MPS. Since I'm always inside the 5SR, with my 2/3 Med, 1 Spi = 1/8*0.4 = 0.05 MPS. However, since I'm a Human with Kings, it's really 0.05 * 1.15 = 0.0575.
1 MP5 = 0.2 MPS.

So, 11 MP5 will equal 20 Spi on a fight of length T seconds, where 0.2*T*11 = (16 + 0.0575*T)*20 => T = 305 seconds.

Okay, close, but not quite. The difference is that I tried to account for the full Spi tick that sometimes sneaks in when you Clearcast a Fireball. Given that with some casting lag, each Clearcast can lead to over 1.5s out of the 5SR, it's noticable.

Anyway, being more exact:

On a 420 second fight with 1 Evocation, 10MP5 is as valuable to me as between 19 and 20 Spi.
On a 300 second fight with 1 Evocation, 10MP5 is as valuable to me as between 16 and 17 Spi.

Yup, nothing to re-enchant your bracers over, but unless someone points out a gaping hole, that's the equivalence.