Hi Macloaded! I am glad you chose a Streamline because I personally believe it is one of FX Airguns finest achievements. Like you I have the .25 caliber version with the walnut stock. In your post you asked for any tips or tricks which may help you get the best out of your rifle...so I will tell you about what I have done to my Streamline and why.
Just so you understand why I did some of these things I will explain that I like to push things to their limit or to failure just to see what gives. Early on I discovered that the JSB Heavy MKI and MKII 34 grain pellets were much more accurate at long range than the 25.4 grain Exact Kings. Like you, my rifle shot the 25.4 Kings at 900 ft/s, but the 34's shot 100 ft/s slower, so I decided to see if I could set up my rifle to shoot the 34 grainers at 900 ft/s also. To accomplish this I removed the factory regulator and replaced it with a Huma regulator that is more easily adjustable, and learned how to adjust the hammer spring tension to accommodate a higher regulator setting.
My Streamline is currently set up to shoot the 34 grainers at an average velocity of 910 ft/s, which equals approximately 62 foot pounds of energy versus the 46 fpe it had when it was new. It has an extreme spread of just 6 ft/s between the highest shot and the lowest shot, which equals a standard deviation of 1.6 ft/s. Of course my shot count suffered badly due to the higher regulator setting so I figured out how to get more shots out of my rifle by replacing the factory air gauge with a Wika gauge that is rated to 315 bar. This allows me to fill my air tank up to 300 bar instead of the 230 bar limit for the factory air gauge and regulator. It turns out that the Huma regulator will withstand the additional pressure whereas the factory air gauge and regulator will not. By filling her up to 300 bar I get 42 full power accurate shots before she falls below the regulated pressure setting, and at 50 yards she will stack one pellet on top of another. The accuracy of the 34 grainers at this velocity is astounding! I got the idea to try this because on the air tube it say it is rated to 340 bar...and I have been doing this now for many months without any air leaks or other problems whatsoever.
I do not hunt anything with my air rifles, I only shoot at paper targets so I truly didn't need to go to the trouble of setting her up to shoot at this level of power...I just wanted to see if I could do it. One benefit is a slightly flatter trajectory and a greater point blank range. For a 1" kill zone my point blank range is from 15 yards to 55 yards...which means that my point of impact is not more than 1/2" high or 1/2" low of my point of aim for that distance. That equates to not having to hold over or hold under, or fiddle with the elevation turret to take a shot at anything from 15 yards to 55 yards, which is pretty sweet for you hunters who many times need to take a fast snap shot at game or not get to take the shot at all.
I regularly shoot with a friend I met from this forum who recently acquired a used Streamline from another member. He asked me to show him how to set up his rifle the way I did mine and of course things being what they are, he is able to shoot his Streamline just that little bit more accurately than I am able to shoot mine! His eyes are 32 years younger than mine, but he also has an uncanny natural ability to excel at everything he does. He goes here by the name gaberossi and I know he would welcome any questions you may have to ask him concerning his new Streamline or the way it is now set up.
The last thing I did to my Streamline recently was to replace my Athlon Midas 2.5-15x50 IR MOA scope with a Sightron 2.5-17.5x56 IR MOA scope...only because I like the floating dot at the center of the Sightron reticle better for target shooting.
Your Streamline is set up fine for what you are using it for and you will probably never want to change anything, but these are some tips and tricks for you in case you ever do! And of course you would have no interest in having the most powerful and accurate air rifle in the whole of Scotland now would ye?
All the best, Chuck