mate of mine has an sr25:
as an aeg he had folk accusing him of running hot (it wasn't, i know this for a fact i put the spring in and tested it myself)
as an hpa it's scary, we ran a "hunt the sniper" game, he set up camp on an island in the middle of a marsh and proceeded to slaughter pretty much the entirety of the attacking group (5 snipers versus 10 regulars and 30 rentals), i was attacking and even knowing the capability of that gun he still managed to ping me at what i thought was just outside the edge of his range.
the m14, scar heavy or svd would also be honorouble mentions.
if you're considering the hpa route it will be pricier, but being a dmr you have some advantages as a lot of hpa's focus tends to be on ultra high rate of fire as responsive semi auto is pretty much a given. pretty much any of the hpa offerings will give you excellent trigger response (especially when combined with a proper speed trigger) over an aeg, my mate's sr is running a polarstar jack engine and it's very good, although you could argue that the fusion/f2 engines might be *slightly* better due to being closed bolt, but frankly i don't think the difference is anything worth crying over.
just check if you're considering hpa that whatever kit you buy has a nozzle/trigger unit available to fit your specific gun configuration (unless it's just a standard v2/v3 length in which case you'll be all right), the g&g sr25 fortunately does seem to be a common one on the list that you can get nozzles for.
the polarstar stuff lets you program what selector setting does what, so aside from physically modifying the safety to move to full auto you can set it to a burst of 1-9 rounds or full auto and set a delay between shots in semi if your site requires a method of preventing trigger spamming. i've not used the wolverine stuff but i imagine their fcu is probably going to be something similar in functionality.