Did you change all your bumper and slingshot switch capacitors? My Embryon was sluggish then it sped up a lot when I made those changes. Due to the large playfield Embryon has some slow lob shots which are followed by very rapid ball speeds for a few seconds. It is an interesting game that way.

Just put new ones in, the old ones slowly turn into resistors as they dry out and cause strange behaviour, a lot of people start clipping them off and not replacing them. You want .05 microfarad-ish, between .04-.06 would do what you need. You want to change all of them since a bad one on a column or row affects the rest of the row or column it is on. Embryon has many caps on various switches, the 4 pops, 2 slings, all the stand up targets and momentary switches behind rubbers. Also check the coin door switches it is best to use them on the coin switches but definitely don't leave any old ones.

I understand what you say about speed being relative. I also have a High Speed and the ball speed is pretty comparable but only in bursts.

Ceramics are nice since the don't dry out like electrolytics. Great Plains is good, I use Digi-Key mostly, these are cheap parts.

You tied a sub into Embryon? That might be a good upgrade for mine. Do you run the high level speaker leads into the amp or tap into the low level somewhere.