HPA is also the PAST of airsoft it evolved in a different direction probably to maintain realism in the looks of the guns, yes the gear box ir relatively unchanged in 20 years but there isnt really much room for improvement on the disign of the gearbox and the improvements have been made by either aftermarket parts or v3 boxes and so on.
I do agree tha tthe hpa systems for airsoft wer awesome and id like to see them still being made (reminisses about the YE MP5's) but i dont think airsofters for the most part want to carry tanks on ytheir backs with remote lines running out of their guns so the new trend is going towards the GBBR's for even more realism trust me if i coud pic up a YE MP5SD6 id be all over it and people would all be like man thats awesome especially the newbies and all the oldschoolers would be like pft been there done that got an AEG never looked back.
I even almost picked up one of thse RAP4's back in the day the m4 one mag fed that you could swap the barrel and load the bb's into painball sized shells and have a gas/hpa powered "shell" ejecting m4 to use both for AS and PB but in the end decided to just stick with AEG's till the GBBR's got all the bugs worked out.
Some interesting info on "classic as" http://www.thefullwiki.org/Classic_airsoft
my all time fave the YE MP5's ( i think i alrdy posted this link) Airsoft: Gas YE-MP5 Underwater - Available in HD - YouTube
amd the i never caught on but could have prolly been quite awesome rap4 http://www.rap4.com/paintball/os/rap...c-261_409.html
and as we see everything old becomes new again amd it may only be a matter of time befor we see "escort" type systems being produced again who knows, i know id buy one or ten lol
And 425fps with .43g bb's thats like 3.61 joules not too many folks wanna get hit with that and there are some snipers that do run 600fps and that is 410fps with .43's so thats not unheard of just not too many snipers are certified/trusted with lvl4 and not too many fields allow for the 200ft meds needed for that fps and to top it off even with the best of hopup systems maintaining a stable flight of such a light projectile at those levles is dificult even over 500fps on .20 like my gun (513fps on .20 or 350 fps on .43) is a lil toutchy to say the least 500-550 fps is about max you wanna go to with .20's to get a good stable flight and at those 500+ powers you baisicly run .36-.43 to lowwer velocities and create a more stable flight and carry more energy out to range to make sniping viable otherwise you may as well run a 400fps aeg with helacial gears and a sorbo pad youd be almost as quiet and still have roughly the same effective range as a 450fps bolt action firing the same .30 or .36 bb's i run .36-.40 with my 512fps on .20's and have an effective range of about 300-400feet depending on conditions like weather/ wind and line of sight 300 is mostly the max 400 is shooting at static targets it takes about 3-4 secconds for the bb to travel the 400ft so shotin at people at those ranges isnt a great idea by the time the shot gets there theis teeth are where their cheas was when you pulled the trigger not verry safe IMO