Since I have changed every internal part out in my Bar 10 I thought I might offer you some advise...
First off, I know its expensive but honestly the best and most noticeable upgrade you can perform on the gun is the Zero trigger upgrade. Trust me, just from a design standpoint alone it makes more since than any other mod. You are going to gain reliability even when using heavier springs and you will also make your trigger pull super light!!! I actually did the upgraded sears first with a laylax 150 before I decided to try the zero trigger. I am not trying to say what you want to do isn't good... its just better in the long run to spend the extra cash for the zero trigger system, ESPECIALLY if you want higher fps since with the upgraded sears you are only going to be able to run a laylax 150 reliably, where the Zero trigger can support much stronger springs. I am running a Laylax 170 right now with no problem and it is shooting around 550 fps with .20's.
Here is the order of mods I would do if I were buying them 1 at a time:
Zero Trigger with piston
Laylax spring guide
Laylax 170 spring
Hard type hop up bucking
Tightbore barrel
Laylax barrel stabilizer ring
Laylax teflon cylinder
Laylax cylinder head
Hop up chamber (haven't installed this yet, but its on my list of things to do
)