Iain,
a quick guide to EP
Magnum...12" long and designed for big game flies. Stiffer and slightly more coarse.
Standard...10" long and designed for inshore/pike/bass flies. This is the one you want for 99% of your flies
Silky...8" long and very soft. I use the red for gills, targets etc (see white fly in photos). Its ideal for flies under 4 inches, but being so soft and limp its not great for Pike. Makes amaving minnow patterns for Trout though
3D in all types...these are "blended" fibres to make up colours. so..for olive green you get green, goldern yellow, a little orange and a few dark green fibres..this allows you to make flies like that "realistic" perch of mine which has a much more subtle blend of dark to light rather than a solid line between colours. the "ocean blue" 3D is proving to be veru good for sandeel patterns
A quick guide to eye size...
If you look at young fish, say Perch and Roach upto say 4 inches, there eyes look large compared to the rest of there body..almost too big...well thats the effect you are trying to get! Large eyes act as a trigger to predators, be they Perch, Pike, Rainbows, Browns etc. The teddy eye on my Perch fly is about right for a "realistic" fly..but i would have preferred an amber rather than a brown one. The red eye on the next one down is a little small for my liking, but I was trying red as a "target" point for the Pike to home in on. The google eye on the white Roach fly is a pure "trigger" eye. Its big and bold and the Pike just love them!
I would use large eyes on any pattern that was being used in dirty water. I would not say there was a "perfect" size for an eye.
I get my google and teddy eyes from a local craft/material shop at a fraction of the cost the tackle shops sell them for. You can get coloured googles as well
I bought a back of 100 mixed colours and sizes (upto 20mm!!!) for 99p from a 99p shop
The epoxy eyes with the flashy backgrounds are from Veniard or Orvis..expensive, but for realistic flies they are perfect.