Velocity for testing accuracy of slugs

I got a 22 caliber Caiman X last year but didn't try slugs in it until recently. When I cleaned it there was a noticeable choke and I just concentrated on pellets. But I had most of a tin of 21 and 25 grain H&N slugs and I was bored so I tried a few groups. To my surprise groups were pretty good. 3/8 to 9/16 inch for five shots at 30 yards. That is worse than it's favorite 18 grain pellet but it's close. So I ordered a sampler which is on its way. But I'm wondering if I should increase the regulator before additional testing.

I get about 910 on 18 grain pellets. I turned up the hammer spring and got them to about 925. The 21 grain slugs were at about 825 with the pellet tune and 860 with more hammer spring. The 25 grain barely get to 800.

These speeds seem OK for pellets but slow for slugs. Should I turn the reg up 10 or possibly 20 bar and see if I can't get the 25 grain up around 900 fps?

A related question is how much difference velocity is likely to make. For pellets I think it is more of a fine tuning thing. If a gun likes a pellet at 800 it will also like it at 880 but accuracy may still improve a little at a specific velocity. If slugs are typically similar to this then I can decide the weight the gun likes best and then vary the velocity.
 
To answer you question regarding speed, yes, you may likely need to turn up the reg pressure to get them even close to the pellet's speed. Slugs have more bearing surface in the shank that causes a lot of drag down the barrel so they inherently require more air to get or keep them moving. It would probably be best to wait unti you start testing the slugs for their initial group sizes before tearing into the regulator. This way you have a baseline to go by to know what increments in additional reg pressure give you as far as results in increased speeds, and, whether the additional pressure and speed either helps or hinders group sizing.